At first i was going to vote for "Town/City" but realised that would only be good it you could go into individual houses and rooms and stuff. I don't dought that some-one could make it, heck i've probably planted the seed already. but the map would have to be huge. it couldn't just be running through the streets shooting, that would be no fun and mainly if someone did make a map this big well it means two things: 1. they.ve got too much time on their hands and 2. who the hell could run it on their system? maybe in the near future but right at the moment it's only possible probably in some secret government organisation.
Any way with all that said it think a nice starship thats compatible for CTF. mabye pirates have half invaded it, but make it smallish. i don't like large CTF maps.