Elisabeth, I have my machines stacked and do not recommend it if you can avoid it. As you pointed out, you really do have to be on your knees to put things in and take things out of the washer. Having the dryer on top and that high means laundry items are always dropping on the floor if you try to take an armful out at one time which is what most of us do. Also, consider your height. If you are not particularly tall it is difficult reaching into the dryer.

Stacked sets can also be a large problem for servicing.

The problem with servicing seems like a legitimate point, but stacking doesn't make the washer any lower than non-stacked. It just precludes you (I assume) from spending the extra $200 per machine to get a pedestal.

The height of a front load washer or dryer, without pedestal, is going to be similar to the front load dryer you probably have already. So judge by that. Personally, I'm getting on in years as well, but I don't have a problem with the stacked washer and dryer. It's more of a nuisance for me to get the dish detergent from under the kitchen sink. If you do get a pedestal to raise the machines, you're likely to be bending anyway to store things in the pedestal. Perhaps not as much, and in different ways, but it's up to you to judge how that will affect you. Or maybe you won't use the pedestal for storage.

Also, if you get a W&D with a light inside, that makes a big difference, compared to reaching around with your hand to find everything.

I'm only 5'6", and don't have a problem with the stacked dryer, either. But then, I avoid taking out armloads. I take out one at a time, fold it, drop it in the wicker laundry basket, then take the next item. Do I drop items on the floor? Sometimes, but not enough to worry about, and no more than when I had side-by-side with a top loading washer.

IMO, laundry should only stacked if you have no room to do otherwise. As dadoes said, you are going to regret it when (not if) you have to call for service.

Thanks, that was very helpful. The point about repairs is persuasive. Also, the builder said he and his wife got a stacked pair and didn't like that arrangement, so they unstacked them. We will have shelves over the W/D - less storage, more convenient, and save money by keeping the ones we have.

For repairs, a lot depends on whether the front panel can be removed for some service; on the pre-built type like the Whirlpool just the front panel can be removed fro belt adjustment (had this done twice at a previous apt.). Other than that, servicing still need to yank out the whole unit for both types of stacked machines.

At 5'5" now, I don't have a problem with my stacked Frigidaire Affinity; one can just use a foot stool when getting the clothes out. I also find getting clothes out much easier than bending over the old top loaders & getting my knuckles bruised; but that also depends on one physical condition.

Most important of all, I cannot have the W/D as side by side because of space availability in a closet! And I found that the price is less than a stacked machine!

Only Speed Queen has a full access panel, sadly the other brands don't have them anymore. Electrolux and Whirlpool made the very stupid decision of removing theirs completely, you can't even get to the trap without major disassembly. LG, Samsung, and GE RightHeight at least give you a little panel to access the trap.

My neighbor bought a pair of stackables for her bedroom closet and she loves it. She does mostly small loads and big loads in the washer down stairs. She was planing on the time when she might not be able to climb up and down the stairs.

By referring to a stacked washer you must be talking about a front load washer.
A front load washer opens exactly like a dryer. Do you get on your hands and knees to use your dryer? If not, you won't when using a front load washer.
That being said, stacked sets are harder to service.

As far as usability goes, and being able to easily access your laundry in stacked front-load machines, I'd like to see someone update a design Maytag used for their one-piece stacked "Neptune" washer/dryer 15 years ago. These used a washer tub that was tilted upwards at the front, and a very large door opening (with a reversible door) that was cut inward between the two parts of the appliance and wrapped over the top, so you could lean forward more than otherwise would be possible. These turned out to be flawed in many ways - they were unreliable, they didn't have an internal water heater, and not everyone liked not having a window in the door - but I've never seen any other stacked FL machine that was so easy to use, and it should be possible for someone to make a reliable machine today with a similar design.

See how the upper was "stacked" onto its own separate base? Not hooking the two together is preferable but not always possible.