tough call. out of my current handguns it would be my S&W 629 4" for functionality reasons. Though, I voted Colt, because I would prefer a 4" Colt Anaconda, as I like my 8" Anaconda better than any Smith I own. If I can only have one, it had better do it all. The Colt Anaconda in 4" is easily packable, its quick, you can hunt with it, its accurate as hell, and its powerful; it'll stop a nefarious human in his tracks, and you can load for bear if necessary, snake shot for little critters and well snakes.. Perhaps a Ruger Redhawk would be a better choice from a durability stand point, but even in that regard the Anaconda is no slouch.
Forgot to mention, its easy on the eyes as well.