I have the bravado, medela (I'm not sure what style, but soft cup, no underwire) cheap-o Wal-Mart, Target and Target nursing tanks. I'm a 40C-DD (depending on if the twins are having a growth spurt or not!).
The Medela is the best for support and looks good under your clothing. It's a basic bra, back closures, pretty easy nursing "flaps". (I've never tried their sportsbra style, so I can't speak to that.)
The Bravado pulls over your head, is SO comfy for sleeping, has snaps for the flaps - not as easy to do one-handed. However, I have found that at night, I can just pull the bra down without undoing the snap.
The wal-mart bra is lacking in support, but for $6, what do you expect? It's fine for around the house.
The Target nursing bra is more supportive than the Wal-Mart, but the one I have in a synthetic blend.
The Target nursing tanks are great - about $18. The material is thicker, not like an undershirt. It is not that supportive, but again, for around the house is perfect. I also use those tanks over a regular nursing bra for belly coverage when nursing in public. Heck, I walk around most days with both the flaps down and am clueless....but the babies are always in a wrap or mei-tai, so no one can see that I'm sagging a bit.
Buy cheap ones now because you have no idea how large you can be! I saw that Wal-Mart had the sportsbra style nursing bras, so you could do those for nighttime. I've never used underwire because of the plugged duct potential and comfort. If you want to do underwire, I agree with ennay that you should wait until 6 weeks PP and your milk supply is established.
The Medela is expensive (mine was about $40, I think) but it is SO durable and very supportive. It looks much better under clothing than other bras, especially noncup ones like the Bravado. (But I love my Bravado for sleeping and around the house, and do wear it in public unless I have a more form-fitting/huggy shirt.
Happy breastfeeding.....it is such a beautiful thing! Maybe you'll be one of those mommas who sheds the pounds like crazy when breastfeeding. Either way, it will be worth it.