I'm not overly fond of barbarians. They're good at hitting things - I'll give them that - but they're also extremely good at requiring enormous amounts of healing (courtesy of their low AC). I don't think I'd ever play one. Too limited for my tastes, I suppose. Or, as someone said a couple of pages ago, too predetermined.
Paladin is close behind. I tried playing one, had a lovely character concept, played it for a couple of sessions, and was eventually bored to tears. Not my type of class. Besides, I never can pull LG right.
I never played a bard, but I think it might be a fun class to play. In a good gaming group. Most of my group don't care much about predominantly role-playing sessions (most of the role-playing involes merchants and attempts to haggle

).
The 3.5 ranger seems like a fun class to play. I'm not a front-line-fighter type of a guy, so I can appreciate the archery feats and the number of skill points. Never played it.
Rogue might be fun, but somehow I always decide against playing one. I love the number of skills.
Fighter is another class I never played, and probably never will. Although I like it much more than the barbarian. More options. But I don't like the limited skill selection.
Monks - I love them. Never played one in 3.X, however - there was always something else the party neede more. But I'm looking forward to it.
I like clerics in theory, but in practice they always fall short. I like sage-type characters, and it's hard to make one with cleric. Too few skill points. That's why I'm really looking forward to trying out the Cloistered cleric from the UA.
I played druid for 8 levels in 3.0, and loved the class, even though all the spells my character prepared came form sources other than PH. The core druid spell list in 3.0 was awful. He also didn't have the animal companion(s). Too much of a hassle. OTOH, the 3.5 druid seems really high-powered. We have a druidess in our party, and she is nothing special ability-wise (Str, Dex and Con are all in 10-12 range), but with her spells, animal companion and spontaneous summoning, she rules the game. Quite literally. The other characters (two wizards, and a ranger) seem pityfully underpowered compared to her.
I like both wizards and sorceres. Wizard has been my favourite class for ages, ever since I started playing. Haven't played sorcerer so far, but I'm planning to, at some point in time. On on hand, the limited spells available make playing him seem challenging, but then I remember the agony I'm having with daily preparation of spells with my wizard, trying to guess what spells will be useful, whether to take damage-dealing or defencive or utility spells...
In short I vastly prefer spellcasters to other classes. The only non-spellcasting class that I really like is the monk. I can do LN, N and NG, but am having trouble with all other alignments.
I voted for barbarian, fighter, paladin and rogue.