I personally love the backplate/wing (BPW) system because its modular and it comes in one size, but can be freely adjusted. You can have a backplate and harness set to your size, but can switch out the wings to suit your diving purposes, very versatile.
The BPW also allows for a more horizontal trim underwater, as compared to a jacket style BC. The air in the bladder doesn't wrap around your body, but it stays at the back in the wing where it should, lifting your back. Having a more horizontal trim makes you more streamlined in the water, and your kicks more efficient.
Another benefit is that you don't get squeezed when the BC is inflated! Though I've got friends who actually like the squeeze because it feels warm and snug, but more importantly, because they can feel the amount of air in the bladder.
Some drawbacks though, the BPW can be hard to pack for flights, especially if you use a stainless steel backplate because of the weight. They aren't flexible as well.
The BPW also doesn't come with built-in pockets, but do come with a few D-rings. Some people purchase additional pouches, thigh pockets or shorts that come with pockets. These add to the cost of the BC. If you don't have much things to stow, you can simply clip them on the D-rings, though you will start to look like a Christmas tree and it sort of defeats the purpose of the BPW's advantage of horizontal trim and a streamlined profile.
Lastly, the cost of the BC should not affect your decision. Choosing one that you will be comfortable in, and one that suits your purposes is more important. Quality and warranty is also rather important, as you might end up spending more on maintenance if the BC is lacking in these two areas.
If not in a hurry, look around, and head down to the shops to try on some BCs! I had a great time visiting many shops and learned a great deal about diving from the people there while in search of my first BC. Have fun!
EDIT: Here's a short article that has good graphics explaining how the BCD affects your center of gravity and trim in the water - http://www.practicaldiver.com/2013/08/why-you-should-choose-backplate-and.html