There are only two classes of toon in WOW, those I've played, and those I haven't played yet.
It's funny, but I've only levelled leather wearers to any significant degree. My first P2P main was a combat rogue, then I rolled a BM hunter. Neither of them got to max level. I rolled an elemental shaman and played him for ages, transferring him across servers and factions to play with friends, got him to 80 (WOTLK) got into PVP, (though I never made the jump to Arenas), but gave up on Wow after Cata. I don't think I even managed to get him to 85.
As for F2P I still have my enh shammy (I tried ele first, as per my old main, but I found him far too slow to play the way I like) and the Sub rogue, which was a coin toss. I also rolled a hunter to see what all the fuss was about, but he's only L4, so there's hope for me yet…
I've yet to play any tanks or plate classes seriously, seeing the abuse new tanks get from other players in dungeons was enough to decide it wasn't for me at the time. maybe in future.
I tried a few casters and healers, again it's something I might try later, I'd like to concentrate on playing the rogue well first.
I've found druids to be really interesting to play, but I've only ever played them badly. And for every type of druid, there's usually another class that parallels it (cat/rogue, bear/warrior).