It depends on what you're looking for in a hotel really. If you want something nice and compact, to save the arms for the parks, Port Orleans French Quarter is nice and easy to trundle around. The other three moderates (Port Orleans Riverside (which I still insist on calling Dixie Landings

), Caribbean Beach and Coronado Springs), are rather a bit larger, but have multiple bus stops around the resort. I'm not a fan of Coronado, myself, because the restaurant operates under a very weird system, but some people like it. I've not done CS or CB on wheels, but the other two are perfectly easy to get about in a chair.
Another option could be to rent a Disney Vacation Club holiday from an owner. I've only done this once, at Old Key West, but we had a lovely time, found the hotel easy to get around and the kitchenette was extremely useful for quick breakfasts and snacks. The only downside we found to the hotel was that it doesn't have a counter service restaurant, but we soon found a way around that
Basically wherever you stay in Disney, you'll find the place easy to get around in a chair. Other than size, there's not much difference in accessibility of the properties I've stayed at (never stayed in the values, or deluxe though). I'm afraid I can't answer on the roll-in shower question, as I can cope without one, so don't want to take the room from someone who can't.