If all you need is DPS...either would work. As to how much overall damage they do, its going to vary dependant upon gear (moonkin itemization is crap), so I'd look more at what you provide for the group. A heavily melee raid would benefit from a feral druid, as you provide 5% crit and some healing for the melee group. However, a moonkin will increase the crit chance of the healers - particularly useful if you have a paladin.
I'm assuming you mean 10-man raids, btw. In a 25-man you'll need a lot more tanks (5 on mag), and you'll need a tank for kara group 2 when you start that, so you may wanna look at feral for those reasons. (Not to mention if one of the tanks can't make it, you can be the off-tank and not force the other tank to solo tank it). And for netherspite, it's best to have 4 people soak up the red beam.
Balance has it's benefits, too. Battle-rez and innervate aren't an issue for either spec, as you can just pop them and go back to form. Hibernate, however, is, once you get to ZA a balance druid will provide incredible CC while the feral druid will require healing. You have the benefit of insect swarm, which is a huge boost for the survivability of your tanks, and outdoors you got even more CC. On netherspite you can still hold the red beam, I'd just recommend you bring a bit of +stam gear (although my resto druid in healing gear held it just fine, even though half of it is cloth).
Basically, it's up to you. Both have their advantages and disadvantages, which I hope I listed fairly lucidly.