I wonder how much of this has to do with proper fit (tensioning of straps) and use of crotch straps. From what I understand, most PFDs, of any type, won't keep you from drowning indefinitely without proper fit and crotch strap. I paid the extra money for the option crotch strap on my Mustang auto inflate.
Proper fit appears to be extremely important. In the book I referenced above they cited a Coast Guard investigation into a drowinging of a man who was a good swimmer, wearing a vest in calm water. Apparently he was a rather large fellow and used a chain to lengthen an attaching strap and because of that the lifejacket boyancy was in the wrong place and he likely drowened fighting the jacket's tendancy to turn him face down into the water.
Inflatabels (automatic or manual) are all the rage, but I've found that for much of the sailing season here in the PNW, the foam vests offer some much needed (and very effective insulation). I do llike my inflatable because it has a built-in harness, and it's easier to wear in the summer but for many months of the year the foam vest is the more useful one for me.
Foam jacket type vests (type I or III) also have the advantate of providing physical protection against blunt trauma. I often hear of broken ribs while sailing, especially crossing oceans while racing. I suspect this is from harnesses that have no shock absorption (credit here to pdqaltair our member who is active in researching this area) but they could also be from falling onto a deckhouse or winch. The foam jacket provides some armor against those brusies, and would also protect the ribs from the impact of the harness itself if you were to take a fall.
Having said that I prefer my manual inflatable and my good quality foam vest types, I will also put in a pitch for cases where the auto inflate could be useful. I think they could be a very handy item to hand out to guests that sail aboard your boat. A non-boater might not be able to find the toggle to pull to inflate when they go overboard, and they might not want to wear a bulky jacket as an alternative. Of course buying an auto-inflate PFD "just" for the guests is an expensive proposition....