We chose where to stay based on location, purely down to my limited mobility. Originally we were going to be in Lion King (building 10) but they could only give us a room at the far end of the building meaning it was too far for me to walk. There also isn't a laundry area in the Lion King section. When I asked about building 1 (Cars) we were given a perfect room (1501) which was the first one on the right as you go in through the main entrance. I'd just whack the wheelchair button and drive straight in, round the corner and there we were! We were literally yards from the building which housed the laundry, a couple of minutes from the car park through the end door opposite the main entrance or the end door turning left from the main building. We could also leave or enter through the end door nearest the food hall/Animation Hall/buses.
Also, having done a tour of the resort, we actually preferred the theming of Cars. DD and I sat down and watched 'Cars' again last night, and it was so lovely to see how accurate the theming in the hotel is - down to the floor lamp in the lounge area (3 cones) - absolutely identical to the ones in the Cones Motel that Lightning McQueen stays in.
If you want to be near the main pool (and the fabulous theming), either of the Nemo buildings will be fine, but you want to try and get the ends nearest Animation Hall and furthest away from the bridge over the lake to Pop Century.