You can really breastfeed in any carrier - for most carriers, you just loosen the carry a bit and drop baby down. If you aren't flat chested (as I am!) you can also lift your breast a bit up to baby so you don't have to drop baby so low.
I have a couple carriers, but most often use the Ergo or Ring Sling. I find the Ergo a little easier most of the time, in general, not just for BFing, but sometimes LO likes to recline rather than sit while BFing, so the RS is better for those occasions.
Re: Best Carriers for Breastfeeding
Breastfeeding Counselor with Breastfeeding USA
Babywearing Guide ** Newborn Carriers
Cloth Diaper Guide
Safe Bed Sharing Info
www.becomingmamas.com