I would.

A long arm is heavy and cumbersome. Therefore, it's more likely to be leaning up against a tree a few feet away when you need it most. It's also slow to the draw if it's slung over your shoulder, or, worse yet, strapped to a pack.

A handgun is much easier to carry, so it's more likely to be with you when you need it most. It also tends to be faster to the draw.

A .454 Casull (like Ruger's Alaskan) or one of Smith and Wesson's X-frames is plenty for bear, if you can hit what you're aiming at. S&W's .500 magnum actually replicates the ballistics of a 2 3/4" shotgun slug pretty closely. Both will throw a 300gr projectile at right around 2,000 feet-per-second.

Here's an article about a guy who killed a ~900lb brown that charged him while he was out walking his dog. The gun used was a Ruger Alaskan .454:

http://www.adn.com/2009/08/13/897940/twig-snap-alerts-dog-walker-to.html