JohnKSa pretty much summed it up in terms of terminal performance: with heavy non-expanding bullets in top-end loadings it's pretty much a case of six in one hand and half a dozen in the other. Because of this, it pretty much comes down to whether you prefer a revolver or semi-auto.
As to your concerns about the manual safety, in an ergonomically designed gun like a 1911, the safety takes only a small fraction of a second to disengage and, with practice, you can fairly easily have it swept off by the time your sights are aligned. The semi-auto will also hold more rounds and give less recoil for a given caliber and size of gun than a revolver will. A semi-auto is also less expensive to produce and thus usually costs less than a revolver of comparable quality though your options will be much more limited in 10mm.
The revolver, however, is not picky in the least about bullet shape. Very blunt bullets like wadcutters can be used in nearly any revolver but may not feed reliably in semi-automatics. Revolvers are also much less picky about the power level of the ammunition so you could use more lightly loaded ammunition for practice or uban carry and full-power fodder for woods carry without the need to swap recoil springs. A revolver can be fired repeatedly at contact distance while most locked breech semi-autos would be pushed out of battery in such a situation (possibly important should the bear already be on top of you). Finally, the revolver can be had in a much more compact package for a given power level than a semi-auto can (.357 Magnum can be had in small, 5-shot revolvers as light as 11.4oz unloaded).
Really, we need to know what kind of bears you're concerned about as there's a big difference between black bears and grizzly bears. A .357 Magnum or 10mm would be an adequate defensive handgun for black bears but grizzlies are a lot bigger and really call for a larger caliber if you can handle it. For grizzlies, the better choices are mostly revolvers as they more commonly come in calibers like .41 Magnum, .44 Magnum, .454 Casull, and .500 S&W though there are a few suitable semi-auto cartridges like .45 Win Mag, .475 Wildey, and .50 AE though guns and ammunition for these will be both uncommon and expensive.
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