For a "short range" (i.e. 100 yards or less) a red dot on AR-15 cannot be beat for ease of use, speed and accuracy (especially when tracking a moving target or moving yourself).
Like most things you get what you pay for. I would get either Aimpoint T-1 or H-1 on Larue mount.
Aimpoint Micro T-1 4MOA/M4 QD Mount Combo 500-009-660 500-009-661 500-009-660HK
Aimpoint Micro H-1 4MOA/M4 QD Mount Combo 500-015-660 500-015-661 500-015-660HK
Buy quality equipment and then you will only cry once.