I have only stayed at one of them, the Royal Plaza. This was 1995. I liked it there very much, and thought the rooms were nice and had no problems during my visit. I stayed in a standard room, by the way. It had a balcony and was quite spacious.
I noticed when staying there that the only real difference between the Royal Plaza and the "on-site" hotels was the transportation. For example, if you stay at Coronado Springs and want to go to the Magic Kingdom, you get on the bus and it takes you straight to the entrance. At the Royal Plaza, the bus takes you to the TTC where you either board the monorail or the ferry to get to the entrance. At the other parks, of course, you go to those entrances. I actually preferred the drop-off at the TTC for the MK because I'm not a theme park commando type who needs to be there the split second they drop the rope. I like the anticipation of using the monorail or ferry, the ceremony it provides. And the ferry is soooo relaxing, going across the lagoon at the end of a long day with Mickey.
Otherwise, I recall that we got many of the same amenities at the Disney-owned resorts, like delivery of packages to your room. But like I said, that was 1995 and if anybody knows of changes made since then, please don't hesitate to update me.
I can't tell you which hotel to pick and why, but the websites others already gave you can help you with that. You basically are staying on-site and some hotels give you nice views of the parks. I think you can find some good deals, too. Some hotels are more expensive than others, obviously, so some comparison shopping is required. It really all depends on what you're looking for in a hotel.
Good luck!
