BP&W systems with a simple webbing harness work great - but aren't cheap.
If you go with more 'traditional' BCs, I'd recommend back inflation rather than jacket style - and the simpler the better. Small bladders are good.
What I'd consider non negotiable when buying a BC:
- It must fit perfectly.
- Weight system must be safe against accidental release.
- It must accommodate all the gear you'd want to bring down with you - but no more. Try to imagine how you'd stow two lights, a SMB, a reel, a slate, a foldable snorkel, a mirror, a whistle and a cutting tool - plus hunting gear and second stages. Some BCs have so many adjustments and straps you can't tie anything to them because floating straps get in the way. Pockets are good if you don't have any on your suit - and if they're actually usable.
Related to BC: look at the 'bolt snap and line' method of stowing gear before buying all kind of retractors and lanyards.