Having a 70 Druid I've had from launch, who is currently a Boomkin, I do not recommend going Balance till the late 50s, as there's little gear to support the spec until then, and even then it's fairly spread out.

Whether you go feral or resto depends on playstyle and the hunter's pet choice; get a good enough tank pet(I had the same boar from 11 to 70 on my hunter and it could take one hell of a beating with the armor/hp pet talents + VERY useful boar snare for kiting in pve and pvp both) and you could probably go resto with few issues; I suggest going feral for the added dps though, as druids basically suck till 40+. Mangle is -godly-, and with Imp LotP you might even heal the hunter's pet a fair bit and will heal the hunter alot if he crits enough ;p

Bottom line, Balance will only be good for Outlands and beyond, Resto only go if you -need- the healing prowess, otherwise Feral's probably your best bet.