Get one that'll last, in my experience that is either Buddy or Seaquest. I have a Seaquest that I bought 2nd hand 10 years ago from a dive school and it's now brown rather than black but it is still fine.
Buddy haven't changed their design much since the Stone Age

, mind you they did recently when they dropped most of their range.
Once you have done a lot of diving you won't really care what BCD you use, you just want something that'll be reliable and last. Hence out of 20 BCD's in my school most are Seaquest some are Buddy with the odd other make for odd sizes.
I currently use a Buddy, it has done 1000's of dives (250 this year), it is reliable and show no signs of wear.