Since this thread has an explicite Pathfinder tag:
The Barbarian, never played one yet but it's the class that intrigues me the most.
Why: it's a mundane class that can not only dish out pain, it also gets tools and defenses against magic, and at least a little out of combat utility by way of skills.
I'd roll one in our current game, but it wouldn't really fit for story/roleplaying reasons.
Runner-up: a tie between Ranger and Paladin.
Paladin: Really greatly upgraded compared to the 3.5 Core version. Less MAD, much better Smite, reasonable class features, interesting archetypes.
Downsides: lack of skills; one of your class features is the ability to lose all of your class features with a single action.
Ranger: can be very satisfying to play as a Switch Hitter. In both Melee and Ranged, you are _almost_ as good as a Fighter specialized in either style, AND you've got a pile of skills that make for excellent out of combat utility (at least at low levels, before skills get replaced by magic).
If 3.5 classes are a thing, then scratch everything I said above, then the Warblade is the undisputed King of the Hill. Hail to the King!