According to me,when one is alone and having 3 opponents alive,the result will depend on one's skills and luck both.In such a scenario,one cannot try to attack them all at once and expect to win.Here we need the ability to surprise and distract the enemy and deliver powerful shots.
So, I would like to go with AK 47 and 2 flash bangs.Flash bangs will be helpful in situations when you have to face more than one opponent alone during an encounter.