The rooms are the same and I'm sure I've seen the prices the same somewhere (maybe US Disney site). Pop and Movies are newer with more Disneyfied theming and are probably priced differently just because they are more popular.
Personally I wouldn't spend extra money as Disney refurbish their rooms at intervals. The All Star resorts are very close to each other. It would be very easy to stay at Music (the one in the middle) and eat or swim at either of the other 2 All Star resorts.