My favorite will probably be Express, I don't know why everyone doesn't like it, its a really balanced map, no team has the "better" side since they're pretty much identical.
Hijacked is another favorite because pretty much the same reason, except smaller so it is well suited for fast action play styles (though I hate this map in Ground War or any other high player game type)
Best game ever: http://www.youtube.com/watch?v=3ZhnGQXWi1U&feature
I want quite desperately to like Express but the side of the map without the trains is just a camper's / sniper's paradise. In every game mode I play you can't travel that side of the map purely because everyone sits up in that house. If it weren't for that building the map would be great IMO.
Hijacked has disgustingly bad spawns but is otherwise not too bad.
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