2 things are equally important.
1: is must be approved for your wieght range
2: it needs to fit correctly.
There are different types of PFDs, the most important consideration is what will you wear. A type 1 pfd has the most flotation at 22lbs of buoyancy, it will keep an unconcious persons head up but is fairly bulky. A type 2 has less flotation and may keep a persons head up, but again is bulky and uncomfortable. A type 3 pfd is what you see people wear when water skiing, or what the USCG wears underway. It will not keep an unconcious persons head up but is the most comfortable and likely to be worn. There are tyoe5 inflatable PFDs that look like suspenders, and must be worn at all times to count. Very comfortable but I don't like the idea that it will open upon contact with the water. What if it doesn't work automatically or for a manual one what if you can't inflate it for some reason?
The best PFD is the one you are wearing when an emergency happens and this is the one that will be of the most benefit to you.
Beyond satisfying any legal requirements the PFD must fit you well and be comfortable enough to ware at all times; it must also have enough floatation to keep your head above water in adverse conditions.
I would say something that is comfortable to wear and doesn't make you feel like a dork.......otherwise, you wont wear it and it does no good!
Lots of people wear inflatable vests available at any marine store..they look kinda like a thick pair of suspenders and can be either manual or automatic ( when you fall overboard) variety.
Also to consider is how well does one swim? A good swimmer might only need a "ski vest" something that gives about 14 pounds of buoyancy.....a poor swimmer might want something that gives 22 lbs ( aType II) or 33 (Type I) jacket, but then you get into high dorkiness.....
high impact if you're in a high speed boat. a neck flotation pad to hold your head up if you are knocked out.