Dont really have favorite maps because after you played some good map many many times it becomes automaticly boring (happens to all maps). I'll rather tell what i have enjoyed playing:
Cube Defence
Skibi TD
Battleships Pro 1.187 (not sure about the name, battleships anyway)
SoulChess
Escape Gay Heaven
Escape Gay Space
Footman Frenzy
Wind&Cloud Open RPG
They are all pretty old maps, some of them still being developed. Dont wanna list the new good maps because there are many of them and only time will tell which stick to my mind strongly enough for me to remember them later (like all those old maps that i listed which sticked to my mind).