.45ACP, without a doubt. while the 10mm is a great round, and can take down a bear, there are issues which make it problematic:
#1 - it's expensive.
#2 - it's not readily available.
#3 - the recoil, as i understand it, is pretty bad.
#4 - from a legal perspective, it would be hard to justify carrying it. a man was found guilty of murder after using it in a self defense shooting. he was in mountain lion territory, i believe, and had to shoot a vagrant. the DA based his murder charge on the fact that he was carrying the 10mm. unbelievable, but true. i' sure someone else kows the story, and will come around with more facts.
i'd just as well carry the .45ACP; it's readily available, affordable, and more socially acceptable (i can't believe i said that about ammo). besides, if you're not a good shot, it wouldn't matter if you carry .22LR or .50BMG.