Apricot is a bit of a challenge as an espalier because it is difficult to keep living wood exactly where you want it in my experience, but if you don't mind a bit of a free form they can be beautiful. Tomcot is the hands down winner for your area according to nearby growers to you who participate in this forum.

Because of the high amount of summer pruning involved in maintaining a 2 dimensional fence you best use blight resistant varieties of apple or pear. I prefer pear above all else for espalier and fence. Pears and apples in espalier form are often available in the ornamental nursery trade for a premium price. Problem is you probably won't know the rootstock or be able to find fire blight resistant varieties.

I would simply start with bare root pears or apples and train them. It would slow you down a couple years but in the long run it is generally a better bet.

Adam's County Nursery carries several varieties of blight resistant pears- you can order ones that ripen at different times to spread your harvest. However, they don't offer dwarfing rootstock so you'd need to give each one quite a bit of room if you order trees from them. I am highly partial to Harrow Sweet but haven't tried most of the newer blight resistant varieties yet.

I planted a two dimensional apple tree fence and I espaliered two pears against a brick wall. My wife calls it my ten year experiment. It's been 5 years and I'm still too new at this to give proper advice, but I'll note my watchouts.
First the squirrels will get every apple, so it's more aesthetics that you are going for.
I'm sure someone in your area will point to good nursery in your area, but you should definitely purchase disease resistant apples. In Atlanta, it's fireblight and cedar apple rust.
buy trees that have the same growth habit. some apples are more aggressive, some are more 'spur' type, some are 'tip' bearing.
How tall do you want the fence? I used a semi dwarfing root stock, M111 because I wanted a screen as well as apples. But most people will recommend dwarfing root stock.
Buy 1 year old trees, 'whips'. they are cheaper there is much more selection and you'll be surprised how fast they grow. Plus it gives you some time to learn 'pruning'.
The pear trees respond to espalier better, followed by apples. I've learned 'pears are for heirs'. it take more time for them to fruit. The apples, you'll have apples in your 3rd season.
The 2 dimensional fence and espalier make it harder to protect from varmits. and if you are in the city you'll be limited on controls.
I have to mention that the folks on this forum are brilliant, and you can learn a lot by reading the various Q&A. but I've learned the most by jumping in.
I hope this helps. It's fun.
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Did you buy from http://www.henryleuthardtnurseries.com/? I am thinking about ordering from them. How did it go?

Thank you for your wisdom. Have you advice on espaliering small ornamental trees? I want to skip the fruit. This weekend I'll be driving fence posts into the ground to create the trellis system. I need to cover about 70'.

Tina,

Personally, if I want to put my extra effort into doing espelier, I would do it so I can have the beauty of the form and the fruit of my labor (literally). I would not do it for ornamental trees as many ornamental trees also have their own issues and diseases. I lost a flowering cherry to soggy soil and a 5 years old Red bud to wilt.

Check out websites of reputable fruit tree nurseries like Cummins nursery, Adam County Nursery, or Rain Tree. They have list of apple and pears that are disease resistant. You just make sure you pick varieties that bloom and fruit in succession so you can have fruit for a long period of time. Bud 9 is a good dwarf rootstock.

I am partial with Cummins because their staff are knowledgeable and answer your e-mail quite promptly. It's a top notch nursery.

Even after squirrels steal all your fruit, you still have a beautiful "ornamental" natural fence :) Maybe, by then, you will post how to get rid of squirrels here.