People usually use the 32qt for breeding colonies if you want to keep a male in with 2-3 other females. Otherwise for individual adults most use the 15/16 qt.
To be perfectly honest...you could put 2-3 AFT's in 16 qt tubs. With 32 quarts you can easily have 4. Leopards 1-2 in 15 qt. and 3-4 in 32 quarts. Just put enough hides for them.
To answer your question though....if your only going to have a 1.1 or even a 1.2 group, I'd go for as many 16 qt tubs as you can afford. Get the 12 drawer sweater rack that Boaphile makes. It's sweet!
The above info is for the NEW boaphile sweater box racks. The floor space is WAY more than your normal 16 qt. tubs. Probably more like a 20 something qt. tub. They are really cool. He has a video on his sight I think showing how much larger they are.