It depends... Do you want to be close to the foodcourt and buses? That's where I like to be. My choice is 70's Big Wheel. That's also a good building if you want to be near the Goofy Pop Jets. The 60's are preferred ($10/night extra).
Check out Chip 'n Dale Express' photos of Pop Century
http://www.fricknfrack.net/pop/pop1.html
To see where the buildings are take a look at the
Pop Century Resort Map
If you want to be near a specific icon here is a list of all the decades and their icons:
50s:
Stairwells will be Brunswick Bowling Pins
Pool The 10th bowling pin
Building 1 Lady
Building 2 Jukebox
Building 3 Tramp
60s:
Stairwells will be Duncan Yo-Yos
Pool Hippy Dippy pool, and kiddie pool
Building 4 Play-Doh
Building 5 Mowgli & Baloo
70s:
Stairwells will be 8-Tracks
Pool Goofys Pop-Jet pool area
Courtyard will feature giant Foosball players
Building 6 Mickey Mouse Phone
Building 10 Big Wheel cart.
80s:
Stairwells will be Rubiks Cubes
Building 7 Roger Rabit perched upon some Dip
Building 9 Sony Walkman
90s:
Stairwells will be Cell Phones
80s/90s pool will be a giant computer monitor
Building 8 Giant Laptop Computer