As noted above, there are basically three types: A fixed, rigid Kapok-type; manually inflatable, and auto-inflating (both CO2). Your requirement not to be cumbersome eliminates the first.
Of the other two, check the regs where you fish. Some states/rivers require an auto-inflate (Type II?)and the pull-cord types (Type IV? I can't remember) are not legal. If you go with an auto-inflate, don't skimp. Some of the BPS and Cabelas models are famous for going off on a humid day in the garage. Mustangs have a great reputation, Stearns just so-so, depending on the model. Check user feedback.

Most important, buy a CO2 re-charge kit with the PFD and TEST IT OUT! I wore a Simms/Stearns manual belt unit for 4 years before I found out the CO2 cartridge wasn't even screwed onto the trigger (a shipping safety requirement). Once I fixed that I tested it and found the neck opening wouldn't go over my head. So don't assume anything -- verify under actual conditions.