Well, I have this "problem" too. I put it in "" b/c I'm not really sure it's a problem at all, maybe just how my body is. One boob was always ever so slightly bigger than the other (pre-prego not noticeable to anyone but me). When my milk came in with ds1, the bigger boob got way bigger and more sore and produced more milk. And, surprise, surprise, ds favored that side over the other. Things are trending that way too with this babe. Both my boobs are like leaky faucets though...
I'd say try not to favor the more sore side except to relieve the extra engorgement. Try to use them as evenly as possible. And just a thought on being sore...one boob might be sore and the other not b/c the child might latch on to each side differently if there is a big difference in shape because of the difference in size.