The Fighter, yes, the humble fighter, because with one class, you can have a lot of viable options.
You can make from a fighter a great Archer, a formidable Two Handed Damage dealer, a efficient two-hander with a shield or another weapon, and a good brawler using an archetype or not, it was not the case in 3.5 but it can be in PF.

I'm not speaking of the versatility of the fighter but the fact that with one class, you have quite a lot of options, for me it is less true with the barbarian...

PF give me pleasure to use a Fighter in the game, the main isssue for me is still the lack of skill points and the lack of class skills really in accordance of a versatile fighter... but anyway, still love this class since ADD1...