Just my humble opionion, but I would say that it has a lot to do with what your used to. If I was to arm myself strickly against two legged animals and do no other shooting my choice would be along the lines of the 1911.
That said 99% of my shooting is with single actions, wether cap and ball or 73' peacemaker. I'm not a super marksman, but the natural pointing of the colt style single action and my almost instintive "cock the danged hammer" makes me feel more comfortable with my 45 peacemaker in my bed side drawer than my hipower or 1911. I know I can handle it and shoot it quikly and acuratly. Or maybe I should just practice with the 1911 more often?
Also in keeping an auto on locked and cocked you still have to do more than pull the trigger, same thing with a single action. A double action has a decided advantage here, but I don't own a DA and don't plan on owning one.
I'm definatly not saying that there are not superior firearms out there, but if you've got one and do the vast majority of shooting with it, feel comfortable with it and can hit acuratly with it, why not? Use what you have to best advantage you can, wether it's a 50 BMG or a rock. And lets face it, while it'd be nice to have an instant reload, how many carry extra mags and speed loaders rite handy? If 5 shots of 45 don't settle it your in deep doodoo.