Talon, . . . go to the decision matrix:
Question: Are they perceived to be life threatening, . . . and/or if I don't engage them, is it probable that I will die or be grievously harmed?
Yes, at leastone weapon is present and/or enough of a verbal threat has been communicated to me that I fear for my life: draw and shoot the closest one first, regardless of weaponry they posess, . . . the closest one is in most probability the most dangerous to you at that moment. The type of shot you will take will be directly proportionate to the methodology of your training, . . . but I would probably make my first shot just as I have cleared leather and leveled the weapon. I would probably attempt to get it up to a reasonable facsimile of a combat stance, . . . but it may not be until all three either are on the ground bleeding, . . . or some combination of some bleeding and some running.
No, at this point, it is only three thugs who have not as of yet made any threats or displayed any weaponry: try disengaging by moving laterally to the best and closest cover. I would try to move to my strong side if all is equal, . . . but then again what cover is available? Getting to cover will also probably separate them, . . . so you will have to contend with that scenario also.
May God bless,
Dwight