I'm sure you'll get plenty of "do a search" responses.
That said, the elite harness used with a bp/w (backplate and wing) is modular and more streamline (reducing drag). It allows you to move things around to allow placement of weights and such to improve trim, among other things. You can add pockets to the harness to place things in, like a spool, back up light, SMB, weights, etc. Or you can just keep it minimal and reduce drag in the water. You can also use a stainless backplate which will reduce the amount of lead you need, plus the jacket is probably has more positive buoyancy so it already requires less....even with an aluminum plate. I currently dive with only 1 pound more using my drysuit than I did diving wet with a jacket bcd.
I used a jacket BCD for about 20 dives. I switch to a backplate and wing and now probably going to sell the jacket style. Some don't like them because a wing can cause you to be face forward on the surface. Personally, I've never experienced that. Having used both, the jacket style is easy in, easy out. It was comfy and had lots of room for stuff. However, since switching I realized I didn't need that much storage. I think most that have used both will tell you bp/w is the way to go. Whether you use an Elite 2, IQ pack, traspac or just webbing. Take your pick.
Just remember, if you buy the harness, you still need a backplate and wing to go with it. Then you will either need to lace weights onto the belt or purchase weight pouches (available in releasable if desired). A good "rig" will cost you a lot more but is soooo much better IMO. There's deals to be had on here, too.
