I would pick a white peach, as these are self-pollinating, productive, precocious, and totally luscious. Check out the varieties at the recommended vendor below. Misterbaby.

Here is a link that might be useful: Adams Co. Nursery

I have a book on growing fruit at home that recommends red raspberries as the best fruit to grow if you're only going to have one. But I honestly couldn't live without my peaches and plums. And if you're looking for heavy production vine fruits may be a good way to go, my kiwi vines are still young but I've heard that when they get mature they can produce more than 100lbs of fruit per vine.

Top choice: fig. they are disease and pest resistant, don't require much in the way of fertilizing or pruning, and are drough tolerant. Once established, they are very hard to kill and will yield you lots of fruit every summer with no work on your part except harvesting. Figs are also one of the pricier fruits if you buy them at the supermarket, so growing your own will save you quite a bit of money. You can easily grow them in pots if you don't live in a warm climate. My favorite that I've grown so far are Black Jack and Peter's Honey.

Second choice, is peach. Home grown peaches are high yielding and the flavor of home grown is definitely better than what you get at the grocery stores. I'd plant an early variety to avoid "peach envy"-- you know, in the spring when the market starts advertising their first crop of peaches and tempts you to pay top dollar. If you have your own peaches coming in then you won't succumb to that madness only to find you paid a lot for so-so fruits. My favorite early peach is Tropic Snow because it's deliciuos and early.

It really depends on your specific criteria, but if you want high production, extremely low care, no spray, easily stored fruit (i.e., just rinse, let dry and throw in a freezer bag), that can be integrated into just about any space with sun and drainage, I'd go with Triple Crown blackberry. I agree figs are also a great choice, but I just like blackberries a lot more than figs. If you don't mind doing some to a lot of extra work, then there are just too many good choices to pick one. You could plant a high number of trees in a small space (high density planting) or plant multi-graft trees (e.g., 3 trees: apple, peach, plum) on dwarfing rootstocks.

Raspberry. They're easy (no sprays), produce a lot of fruit, will spread on their own so you don't need to worry about spacing (just containment), they taste good, and produce a long time. In a different climate I might chose peach because home grown ones are so much better than store bought, but here in Wisconsin peaches are much more difficult.

Peaches and figs seem to be good choices! I would love berries, but we already have some wild black raspberries growing on the edge of our property. I've read that you shouldn't cultivate berries until you get rid of the wild ones, and that will be a while. There's a lot of poison ivy around them, so I can't just dive in and rip them out. Or pick them, for that matter, which drives me nuts. Ripe berries dangling just out of my reach!

Thanks for all the advice.

I've got wild blackberries and black raspberries all over my property as well and it would be nearly impossible for me to get rid of them. TC's are disease resistant and I have not had any problems in the 4 years I've grown them. Ideally, yes, it is a good idea to get rid of the wild ones if you can, but in most of the country that just isn't practical. I'm fairly certain that 99% of non-commercial bramble growers in non-arid climates have wild brambles somewhere on their property. Also, a few well-timed herbicide sprays could probably knock out that wild berry and poison ivy patch

There's no straightforward answer to your question, because we don't know whether you are prepared to spray, build trellises and so forth. Here are some quick pros and cons:

Peaches in PA - severe insect pressure, spraying probably will be necessary.

Figs. Zone 6 PA will probably require wrapping them for winter and many varieties may not ripen before the cold comes.

Raspberries: generally trouble free and tasty.

Blackberries: Triple Crown are great and super productive, but you will probably want to put them on a solid trellis.

Asian Persimmons: relatively trouble free (no spraying needed), and you might be able to find cold-hardy varieties that would work where you are, e.g. Sheng.

Blueberries: pretty trouble free and productive, but you must have acidic soil or make you soil acidic. Will need to net to keep birds off.

Sour cherries: I've got good yields here in Maryland with no spraying. Not good for fresh eating, but make great pies. Montmorency is the standard variety.

No problem building trellises. I don't mind spraying once or twice if it's not outrageously expensive or outrageously toxic. I know little about spraying, but I'm willing to learn.

I've got a lot to think about already....thanks!

I'll echo the comments about peaches and brambles.

Peaches taken care of will start to fruit the year after planting, which is a big plus. As mentioned, there is more difference/improvement in homegrown peaches vs. many other tree fruits. However, peaches will probably require more than 2 sprays in PA.

At least one poster on this forum bags his peaches with cotton drawstring bags to avoid some spraying on stonefruits. It's not feasible with lots of trees, but I'm surprised more people with just a few trees don't utilize this practice. Spraying is work.

Brambles generally don't require any spraying and also fruit the second year.

Figs are definitely iffy in zone 6, but I'm sure they're easy care in CA.

Wow, what an interesting question! I'm not sure what my choice would be off the top of my head (but I am leaning heavily toward pawpaw), but this is what my process would be...

Like you have done, I would first exclude plants that take alot of care and are not too productive... I would also exclude those I could find in the wild (which in PA could be a whole lot) AND those that are commonly grown in the area.

So, anything you could easily obtain within an hour drive, I would exclude, and focus on something really rare and unusual... maybe hardy kiwi as peachymomo suggests.

Have fun with it

Strawberry, just my opinion.

I could make a case for:
White peach--most productive tree, with really good fruit.

Apricot--unbeatable combination of looks and fruit.(nothing in the stores compare).

Grape--I gave up on it and decided it was purely ornamental, then caught a glimpse of blue under a leaf last August. Just a juggernaut in the growing department.

how about something that has a long season?

mulberry
everbearing strawberries
primocane black or raspberries

This isn't helping me narrow it down....now I want to put ALL the suggestions in!

Lol, I understand completely! I thought I was done planting my backyard orchard until I came here for suggestions of things to add, now I'm back to the drawing board finding places to plant more trees and shrubs.

The fruit I look forward to the most every year is the apricot. But by the end of the season, I've had enough of them.

I can eat an apple, or two or three, every day of the year, so if I could have only 1 tree, it would be an apple--- maybe with a few different varieties grafted onto the tree.

Blueberry or raspberry...........my fav things to eat, love em both!

Where in Pa do you live? I grow 35 different types of fruit and several varieties of each. My expertise is figs and have over 250 varieties that I have been evaluating in our climate.
I don't like spraying, so I removed my apples and plums.
My best producers are Jujube, Asian Pears, Asian persimmons, Figs, Blackberries, Currants, Mulberries.

Bass

I'm in Western PA, near Pittsburgh. Two hundred and fifty?? Wow! How do they do? What do you do to protect them in winter?

Your Asian Pears don't need spraying at all? Are they productive? My family loves them.

Everyone has me sold on the blackberries or raspberries. I'm definitely putting a patch in! Possibly some strawberries, too.

I think I'd still like at least one fruit tree, though!

Ajourni, for your zone the answer is mulberry, although you could experiment with aronia or serviceberry (large bush). Fig and peach have optimal ranges farther south. Mulberry is a tough weed tree, no spray, long season, and the fruit can be picked by spreading a tarp under the tree and shaking the trunk.

I'm thinking about Caroline Raspberries. I'm trying to learn more about brambles, but it sounds like for my zone everbearing raspberries are the best choice in brambles(?). I'm still researching it.

My father had a row of red raspberries planted that he mowed down every year, so they must have been everbearing. They suffered from the WORST pest damage though....something devoured every single berry just as it reached the peak of ripeness. It happened at exactly the same time each day, which, oddly enough, happened to coincide with the time I came through the yard on the way home from school. :)

We have a mulberry on the adjacent property which is legally zoned a "road," but is actually the wooded side of a hill. Since nobody owns it, we feel free to mooch all the berries. It's a terrific tree, but since we "have" one I'd like something different.

Lots of choices given, but if you only plan to plant one fruit, I would recommend Asian pears. These have broad appeal, fruit precociously and can be productive. More importantly, unlike most of the other fruits mentioned, they can be kept refrigerated and maintain good quality for fresh eating nearly year round (most of the other fruits would need to be frozen or dried or canned if not eaten soon.)You will most likely be able to grow decent quality fruit without any sprays though you should learn to identify fireblight and pruning techniques, and it would help to be familiar with the appearance of the diseases and insects that affict pears. You will need to plant two varieties for pollination, but these can be planted very close to one another so that they can take up the space of little more than one tree.

what about codling moths with asian pear?

Codling moth can be a problem with Asian pears, and if you know that these insects cause damage locally, you will probably need to spray these trees. If unsure, check with the county extension agent. Another bug that may interfere with spray-free Asian pears is the brown marmorated stink bug, the arrival of which appears to be changing the requirements for growing decent quality fruit.

Would bagging the fruit help against codling moth and stink bugs? We definitely have stink bugs...we've been finding them in the house all winter. Yuck.

I've been attacking honeysuckle like a crazed person the last few days, hoping to make room for more fruit...since it's so hard to narrow it down.

In So Cal I suggest white peaches/nectarines or sellf fertile Apricots. Easy to grow after that I like Plums, then Pluots . Pluots for me are harder to get them cross pollinated. After that I like Kishu Mandarins, blueberries.

I've had to deal with both codling moth and stink bugs on Asian pears here in Maryland, and bagging the pears does indeed work. There are plenty of discussions on Garden Web of bagging using plastic sandwich bags.

Don't do it it's a trick. I moved into a house with a few apple trees in the woods/ old overgrown fields and bought the wife 2 reliant peach trees. We now have 300 fruit trees and 4 ac of blueberries. we have 3 ac of tilled gardens and this winter she said "I want a small garden to try some giant pumpkins. Out comes the chainsaw and backhoe again. Why didn't I buy a 1 ac intown lot instead of an old 70 ac farm.

A p.s. to my above post. I had to sell my salt water fishing boat to buy a real tractor "you don't have time to use it now" I had to sell my snowmobile to buy back hoe for said tractor"your getting to old to have to go fast" 2 years ago she said " you don't need to go wilderness hunting you have enough here to keep the deer / rabbits ect away from my gardens"