I'll take the unreal engine for games with large exterior sceneries like jungles, deserts, pyramids, etc.
Doom3 engine excels in "mostly-interior" type games where lighting is the main focus (for mood creation).
Source engine is very good for both type of games, but I don't feel the pull towards it. Atleast not as much as with the other engines.
So I really can't say here. But for the sake of the unambiguous poll question, I'll choose unreal.
PS: I think u can ask the mods to change the poll choices. Just PM them.