I'm going to have to say Feral. My main 29 is an Rdruid (FC), and I can agree that even as resto druids should not be able to hit as hard as they do. However, Feral is on another level. Mechanically, they are able to lock you for a short period and deal a potentially lethal amount of damage within said time-frame. You then combine their mechanics with available gear and enchants, which equals a world of hurt. There is no other class capable of hitting the numbers that Ferals can, and I'm not just talking about Ferocious bite. Shred can easily crit for 1100+, and they can get 2 or 3 of those off in a row before the bite even comes in. They have amazing mobility, decent healing capabilities, and if you're playing a Night-elf, re-stealthing is just icing on the cake as they can double-lock you. For me, as an FC (primarily), it's a nightmare. The stacks pile up in WSG and that's GG if a feral catches you...
Yes, BM is OP, but I don't think they're as much of a pain. In order to maximise their bubble, they stack AP & sacrifice HP. Because of this, more often than not, I see BM's get dropped by range before they can get guard up. Not to mention, BM's cant sneak up on you, stun you for 3 seconds, or burst away into a stealth. Their healing is hard-cast (for the majority), unlike Ferals who can insta-Healing Touch after a finisher.
I can't ever justify speccing Feral for PvP purposes. It feels too cheap. I can however validate playing a BM, as range DPS can easily take you down if you're without a healer. Obviously, the opinions are scattered on this. I see the validity in both arguments, but I suppose my bias extends from being crit for over 7.5k (WHILST I'm in bear form... with stacks ofc) by Ferals; a feat that BM's aren't capable of doing...