Mage - If played well you can 1v1 any class without a problem.
Rogue - Pick your fights that you know you can win and you can escape easily.
DK - If you play unholy you have an enormous set of tools to gain life, you can rape most casters (not really mages unless they are bad).
Hybrids - I think Ret/Enhance would probably be fun to play and shouldn't die too easily in BG's. (Gwolf/Bubble offhealing and running).