What I enjoyed playing so far:
Fighter. So far, it was always fun to play a fighter, though I think there are a few weaknesses:
- Difficult terrain proves difficult to handle. Climb, Jump and Swim are great (and you can really show off if these become relevant), but the lack of Balance can be noteable. (But I actually played a Fighter with that skill, and it proved a good idea.)
- Outside of combat, the Fighter feels nearly useless (unless involving, climb, jump, swim).
- Flying opponents suck.
- Large Opponents suck if you didn't waste your feats on the Weapon Focus chain.
Oh, and PHB II rocked.
Warlocks. Even if a bit "boring" (yet another sneak attack), the "always on" spells are really nice and make your character stick out.
Sorcerors. Blasting people is fun. The lack in versatility has to be compensated by other characters, but the core is great.
Wizards -> Loremasters. I just like going this route. The knowledgeable wizard archetype plays well.
Rogues. The only class that can participate nearly everywhere - except dungeons infested with undeads, I guess. Luckily, my Rogue could avoid this. The biggest problem is there are too many good skills.
Druid -> Shifter. Becoming any type of creature, any time, that's something I really enjoyed. Sometimes it's just fun turning into an Elephant or Delver.
Classes I don't really like, but still managed to enjoy for some time:
Cleric: I think buffing as a Bard is more fun. Clerics tend to buff before combat (with the long-lasting spells), and thus in combat, you're either buffing yourself to get into melee later, or you go around healing. I think my best experience so far has been focusing everything I got on healing (Radiant Servant of Pelor), and not care much about melee combat.
Classes that I wanted to like:
Monk. They die too fast, and don't do enough in combat.
Other classes didn't stick out particularly for me, though I think I enjoyed them all.