I don't play FFA much but Hangar is a good map as it's nice and bright, there's open areas, and lots of good hidey holes, etc. but it's not too big so it doesn't benefit the snipers.
I get annoyed with some maps where the colours are very similar (like Downfall) or it's too dark (like Makin) as it's harder to spot other players.
I remember playing FFA once (edit: or it could have been TDM - it was quite a while ago) on Outskirts (trying to get the Survivalist challenge I think) and managed to hide in one of the buildings at one end of the map - no one came anywhere near me for the whole length of the game. It's just too big!
I'm used to the slow pace of S&D so FFA on Dome would just be a blur to me - I'd always end up getting my butt kicked.