Back plate and wing.. and soon to be Drysuit. When I get cold in the water, after so long of being cold, I literally can't think straight. I'll be ordering a dry suit very soon, and so far the experience I've had diving one has made a world of difference.
I was diving a back inflate BCD, and I got BP &W for my birthday. All the clutter and whatnot from my old BC is gone. What a nice change. I didn't need all the extra stuff (pockets, d-rings, etc), especially since I'm headed down the technical [-]tunnel[/-] drain hole.
fixed it for ya, before some one flames you bad!
Seriously, even my gf, who has no designs what-so-ever for tech, has decided the plate, harness and wing just fit her needs so much better, and give her better control of her body in the water.