If you practice a lot, the 1911.
But I voted 686 because you can start with .38 specials and work your way up to .38+Ps or .357 Magnums as you prefer. You cannot (relative term) jam the revolver, as opposed to 1911s which require much maintenance and are a pain in the @$$ to clean when you aren't used to it. Get a 686+ and you've got about the same amount of rounds, and although the .357 Magnum rounds are inordinatley louder they will both split your ears and in a life or death situation I'll deal with the "EEEEEEEEEE" in my ears for a few hours. If I just used my firearm then I've taken a life and therefore I have bigger things on my plate. When it comes to "Tacti-cool" the 1911 is tops, but for basic defense? My money is on the magnum, especially if you aren't accustomed to proper cleaning and maintenence. Not to mention how finnicky most 1911s are with finding the right magazine/JHP ammo combination that won't cause some wicked jams.
Before I get too many nasty responses, I like the 1911 "better" myself but for these purposes, if you're going to own one... welll, I already said it.