The thing that I find with the maps is it depends on the players I'm playing with. When it's Pard, Joe, Breli, and/or Red, I usually love Train, Hang'em High, Dawnfort, and Nonamecity. With newbs I love trying out Dry, it's a great map to start with. (it's also the first map I played of the game.
)
Coyote Bluff I love in appearance but I've not yet had great experiences on it (mostly due to only fighting bots or just one or two people, not a nice sized group). The br_coyotebluff game yesterday was probably the best I've had. I've spent more time filming on that map than actually playing it.
Oh yeah, I do love Tillian because I have fond memories of pwning everybody on that one.
Not that I can do that again. >_<
I agree with Pard, though, it's really hard to choose a favorite map. There's ones I may prefer, but it all depends on situation and mood and the circumstances of the players.
A poll might be good for figuring out what style of map works best in the game, though.