I say draw, shoot the closest, armed assailant as you're backing up, and then run the other way. Hopefully, the other two won't pursue you if you have a handgun. If they do, try to bottleneck them or get around a corner or anything, get a little distance and force them to approach you one at a time, so all three of them can't swarm you and stab or beat you to death, or tackle you and kill you with your own pistol.