I wouldn´t say there´s any class I don´t wanna play. It depents on the decks and possibilities with this class. Before Even-Shaman I totally disliked Shaman and never want to play this class. Atm I don´t like Druid very much. Testet some Decks a few month ago, when he was T1, but couldn´t find one I really wanna play and which makes much fun for me. The class I most like is rogue. I played very much different decks and liked them very much accept Questrogue. Thats just too boring for me. Now I´m waiting for Druid come along with a deck I really like. But this could wait, as Druid was so long time in top tier list. Let´s give him a break. That´s totally ok for me.
Warlock, Priest, and Mage are typically the only classes I play. It's not that I haven't played other decks, I'm just mostly F2P and I've found, choosing a couple classes that you enjoy is the best way to be able to play and not miss out on decks.
I play every class. My most played class is Hunter with 618 wins and my least played is Shaman with 76 wins. I have minimum 200 wins with every other and I have 500 with Rogue and 376 with Priest. I play a class for like 50-60 matches, get bored of it and switch to another. It keeps the game fresh.
As for Arena, I tend to play classes with higher winrates at the time, but mostly focus on control decks, so Priest is my baby. I just love drafting 2+ Mind Controls and making people salty ;)
I used to play Warlock, Priest and Druid A LOT. But I have them all golden (plus Rogue, Paladin and Hunter) so at the moment I'm focusing on the ones I don't have golden: Warrior, Shaman and Mage especially.