Take your time and do your research.
Try it out in a pool and see which is best for you.
For example I have tried both and prefer a back inflate BCD over a jacket style.
No matter what you go with you should purchase from a trusted source such as a dive shop that is going to service and stand behind the gear.
ebay is great for deals but not when it comes to something you are going to depend on for life support.
On a final note some of my favorites include...
ATOMIC split fins and regulators, Aqualung Balance BCD, and Henderson or BARE for wetsuits.