One of the problems with the Pop Century is it's a huge hotel, the biggest at Walt Disney World. There are almost 3,000 rooms (2,880). That's more than the Contemporary, Polynesian and Grand Floridian Resorts combined. Since there are only 10 buildings at the hotel, that means there are almost 300 rooms in each building.
The buildings are huge. For example, the 60's buildings are the closest to the the main building (Classic Hall), but if your room is in the far end of the 60's building you'll be a long way from Classic Hall.
Also, the 60's buildings are a long way from the parking lots. So if you have your car at Disney World, it can be a long walk from your room to your car. If you have a car you'll probably want to be in the 50's or the 90's buildings. (We really liked the 50's when we stayed there.)
Another big draw at any hotel are the pools. The Pop Century has some really neat pools. There's the Bowling Pin pool in the 50's building, the Hippy Dippy pool in the 60's building and the Computer pool in the 90's building. The 70's buildings don't have a pool.
Disney does have preferred rooms at the Pop Century. They are the rooms that are closest to the Classic Hall. The buildings that have preferred room are in both the 60's buildings, the front half of the 50's and 70's buildings closest to the Classic Hall.
So which is the best? We like the 50's and the 60's. If you have a car pick the 50's if you don't the 60's is better. If you want to be closer to the Classic Hall spring for the preferred room and request the 60's building. If you want the closest add a pool view.
You can request a specific building, but Disney doesn't guarantee any request.
I'd really suggest you give my friends over at Destinations to Travel a ring. They can help you pick the best building for your stay. They can also help with everything else you'll need for your trip.