To add to what Greenie says... the small, simple, open maps are the maps where you're most likely to get support from your randomly thrown together team on a public server IMO.  For the same reason that flag runners hate them - everyone (on your team in this case) should be able to see you and help you.  

I like skyscraper and there's a bunch of maps on the 100+ map private server I'd love to see tried out.  Big ones mostly though.