As a solo tripper I take a zero tolerance approach with myself.  I only wear it on the days I want to live.

Wear it, regardless of what you buy.  If you don't, then if you dump you really do deserve the results be they a soaking, injury or death.  Have a thought for those that love & care for you, at least the ones you love in return.

I'm a big fan of passive solutions for saving my life.  If you have to push a button or pull a cord to make it work, it's less than ideal.  Better than nothing, but not as good as something that works regardless of your state.  If you hit your head & are not thinking straight or out cold, what good is that pfd?  You wouldn't bungie jump while the operator says, "You go ahead, I tie the rope off as you fall, don't worry, I won't be late." 

There's a commercial going around of all the stuff a particular car does in the event of an accident.  Really well done for illustrating how we're not thinking of anything other than, "Oh crap!  Oh crap!  Oh crap!"

You get what you pay for.  A $20 pfd is likely bulky & uncomfortable to wear and might not last a long time.  $100 will last & be comfortable enough to wear.

My preference is for a kayak style, more flexibility.

On a hot day I like to turn mine upside down & wear like shorts for swimming.  I can just sit there and bob on the water, toss a ball around.

It's exactly like seatbelts in cars and helmets for motorcyclists. 

Any deaths that result from not wearing a PFD is gene pool maintenance.  I'm always sorry for the survivors of the deceased, but in reality we're all better off without those defective genes.