Infection hands down i can think of many fun things i can do with infection that i can't with other gametypes besides its fun trying to balance it
Symmetrical CTF, Territories, Slayer, and occaisonnaly oddball maps. That sounds like a lot, but the way I design them is very similar.
here's a list of what i would most want to do in order (1st is my first choice) Small competitive maps, with lots of depth to em. Infection Aesthetic Race tracks Large competitive mini-games
Thank God for diversity. It would have blown to make this thread and have everyone say the same thing.