I enjoyed playing a cleric, druid, and ranger. I did not enjoy playing a Fighter or a Rogue with a few levels of fighter. I played a Paladin/Archivist gestalt for a few sessions, but I did not count it in my vote, since that is a whole other beast entirely from single-class paladin.
I think much of this is dependent on my attitude about the game and the level of mechanical knowledge and munchkinry that is necessary to play an effective character. If I want to play a druid who focuses on mounted combat and hardly ever uses wildshape or summons creatures, I can do that and still fill the role of backup melee and healer (and I have). The druid is flexible enough, and powerful enough, that this sub-optimal choice still works.
In my experience, it is a lot easier to mess up a fighter, which is a shame, since it is often the class given to new players who are just learning the game. Part of this has to do with the fighter's lack of options. Fighter's have to fight well, they don't have any skill or spell options to fall back on. Conversely, they offer lots of feat choices, but only a few of those options are actually good at helping the fighter do his job effectively. It is all too easy for someone like myself to settle on a feat combination that looked cool, only to find out that it is utter rubbish in play. As the old saying goes, it gave me just enough rope to hang myself with.
The same thing can also be said for spellcasters, but aside from the sorceror and bard, they can actively change their spell selection during play. Even if it costs a wizard money to do so, he can add new spells to his book, and a divine caster who picks the wrong spells one day can just pray for different ones the next (if he survives his mistake). Fighters on the other hand, need to be re-written, switching out feats, making sure they meet skill and BAB prereqs for the replacement feats, perhaps reshuffling ability score points or even ditching fighter levels for another base class or PrC. In the end, the fighter just takes a lot more work and mechanical knowledge to not screw up. There is no safety net, no fallback, no guidelines in the class itself for how to do it well, and as a person who doesn't want to put a huge amount of time mulling over my build, those are things I want and like to have with a class.
Robert "Then Again, I Probably Would Have Went With TWF and Monkey Grip Anyway" Ranting