Probably depends as much on the type of sand and grass around the greens and whether you tend to swing steep or shallow. I have several versions and will swap them out depending on where i play that day. Best option would be to go through a formal fitting. If you don't want to do that, a good general rule will be to pick a high bounce if you tend to be a little more inconsistent and low bounce if you always make good contact or play very firm sand and tight lies.

Per the website, the Vokey wedges are designed to be very specific to one's swing shape and the consistency of sand in play, much like Dale described in his post. I did not go through a fitting, but have been gaming the SM6 58-degree K-grind. The K-grind is described as "most forgiving," which for someone who is short-game challenged as myself has a special appeal. So far I've been very pleased with the results!