For me there is only one choice when it comes to druids: Feral.
I know balance can put out good DPS and that restoration is good for PvP healing, but neither is as much fun as being a feral druid.
With my feral druid I need one kit (I keep two, but I rarely switch out of my tanking gear). I don't need to switch out of cat form when I'm grinding because Improved Leader of the Pack means I am healing myself for about as much as the mobs I am grinding are hitting me for. I can two-man-tank UBRS and LBRS without a healer for the same reason. Mangle packs a meaty punch and if Omen of Clarity pops are the right moment (as it often does) I can Mangle four times in a row and then either Rip if they have over 3k health left (highly unlikely) or Ferocious Bite to kill them off (max crit on Bite for my Ghosthoof so far is over 3.2k). I often kill level 70 mobs before the 10 second cool down on my Prowl is ready, which is only a problem in very crowded areas.
Tanking as a feral druid is a dream also. With Feral Charge, Mangle and Swipe I find re-acquisition of threat to be easy, while Mangle, Maul and Lacerate mean keeping threat is a breeze. Combine these abilities with Frenzied Regeneration, so I can heal myself in a pinch, Improved Leader of the Pack, meaning I am healing myself for around 600 - 750 (depending on buffs) each time I crit, and the Primal Fury talent, giving me 5 rage each time I crit, and you have a threat generating machine. I can even hit myself up with Regrowth (and Rejuvenation if I feel the need) before I pull, which allows the healer to hold off healing for those precious few seconds at the start, thus keeping all the agro on me.
In my opinion, all of these points taken together make feral druids the best specialisation for the druid class.