I have never had to stop a bear attack, but I do spend some time in bear country in Montana and farther north.
Apparently, when people have been attacked by bears, it's not unusual to end up on the ground rolling around with the bear. In the situation, I would prefer a double action revolver. Also, a bear gun isn't going to do much good if it's sitting on the truck seat wheile you walk into a campground looking for a camping spot. I like my Smith & Wesson Mountain gun with it's 5 inch barrel because it can stay on my hip all day and not be overly obtrusive.
While working in a gun store years ago, we had enough Taurus owners bring guns back with locked up cylinders to allow me to have any confidence in that brand.
Based on accounts of other people's bear attacks, if given a choice, I would much rather try to stop a bear attack with bear spray than with any handgun. Just going with the statistics on that one. Oh, and the fact that it's not unheard of for people trying to stop bear attacks with firearms to shot the wrong mammal.