I'll add another vote for Spinlock, they are well designed.
@Sailfanatic mentioned crotch straps, and although I've been guilty in years past of thumbing my nose at the idea... a couple incidents the past couple years opened my mind... now, count me in the camp of how important they are.
I did the US Sailing Safety @ Sea this spring, and added an aftermarket set to my old West Marine Offshore. Jumping in a pool in full foulies, I was amazed the difference. I was able to adjust the tightness while floating, and it really helped get a comfortable position, without fighting to keep the lifejacket sliding-up your face. Was night and day difference when I unclipped them.
If you don't have them, only costs $16 to add them to any inflatable. And, I learned that I can leave them a little loose for comfort, and easily pull them tighter if I ever go in. So there is no excuse about comfort.
They will be required on our boat for distance racing starting this year... I will buy them for anyone on my boat that thinks $16 is too much.
I encourage everyone to consider adding/wearing them!