Every outdoorsman has his opinion of "best" handgun for bear defense. I've figured out that it doesn't get better than a Springfield Armory TRP .45 Auto. I'm sure a TRP 10MM would be as good. However, FOR ME, I prefer a .45 Auto.
I've owned a 6" 629 .44 Mag. That was one huge gun. It was not comfortable to carry. I was and am not recoil averse. There was no way in you know where that I could rapid fired that gun. I called it a one-and-done handgun because of it's recoil. Assuming I were able to get it to battery (out of holster and on target) at a charging bear, I'd most likely have time to fire one round. I'd pay to watch anyone rapid fire a 6" .44 Mag with authentic magnum rounds. It was too big and too slow to battery to have utility FOR ME. I sold it with zero remorse.
I tried a 4" Model 586 with 180 Buffalo Bore hard cast bullets. It was so close in weight to my Model 629 that I couldn't notice weight differential, assuming one existed. 180 gain Buffalo Bore .357 Mag ammo has substantial recoil. Same conclusion: there had to be a better way.
Reloading any revolver, especially under stress takes too long.
When fishing the Eastern Sierra and the Rockies, it's all about comfort and portability. A full-size 1911-A1 handgun has to be the most comfortable big bore handgun to carry all day on my strong side. In a good holster on an authentic gun belt, I can forget it's there.
Now, rationale for choosing a Springfield Armory TRP .45. I did extensive research. Other than going with a custom made guy, there is no factory production gun that's superior to the TRP. Mine has been unbelievably accurate. It is as close to 100% reliable as as mechanical device can get. Mine has been 100% reliable.
Here's where it gets better. Not only is my TRP easy to carry and lightning fast to battery, it has the most devine natural point of any handgun I've held: it practically points itself, and it's superbly constructed. Its Armory Kote finish is impervious to thermonuclear detonation. Well, that might be extreme, but the point is conveyed. To write that it's well-made is a slight to it. It was crafted to precision. It doesn't rattle. It's slide-to-frame fit is perfect. To get better, one would have to go with a SA Custom Shop 1911-A1. I found during research prior to buying that it's such a superbly constructed handgun that some owners, after installing a 24 pound recoil spring, fired 255 grain .45 Super Buffalo Bore ammo out of their TRPs without a single malfunction. This ammo is much more powerful bear defense:
https://www.buffalobore.com/index.php?l=product_detail&p=397 than any 10MM load. However, I have no intention of firing that ammo in my TRP.
When I'm in wilderness areas of the Eastern Sierra where there are more black bears than trout and the Rockies, I'll load my TRP with 230 grain Fed HST LE +P ammo. Only mythical bears could take 8 rounds of that ammo and keep on ticking. For bipedal vermin, I'd good with standard pressure 230 grain ammo, even ball ammo.
If it were necessary, I could reload another 8 rounds in my TRP within seconds.
Speed to battery, ease of carry, ability to completely field strip my TRP miles from nowhere if I were to drop it in mud requiring thorough cleaning, its vaunted reliability, its unbelievable accuracy, speed of reload, and the extremely versatile .45 Auto cartridge made my choice of bear defense handgun a no-brainer.
I'm completely good with others' choices. After all, every outdoorsman has to choose a handgun that's perfect for his intended application.