My favorite is the soulknife. Followed by the warlock (3.5 I know). Mix the two together with hideous blow, and you have a up front line fighter that is never without a weapon, and hits harder than any fighter I have ever seen. Then drop elocator on top and you are doing damage from every angel you can come up with.
I have played a summoner and an alchemist. Both classes are fun, but easy to break.
For my summoner my edilon was tanking way harder than the fighter, and dealing more damage than the rogue could even come up with.
My alchemist puts every character I have ever played (save one) to shame in damage per round.