Apart from suggesting to look up "the best" threads in the rules...
Err, i think the Mi-8, Mi-24, Mi-28, Ka-50/52 and AH-64 have it beat easily, as far as armament goes. W-3W, W-3U, IAR-330, AS-532AL and SOCAT too probably. It probably carried the most armament at its time though.
Only the two 20mm guns and the 19-round rocket launcher were capable of engaging an enemy at range - i.e. outside the enemy's organic MG range. The M3/M24 20mm gun was a WW2 HS.404 copy with known reliability problems that most users - including the USAF and USN - phased out in the early 50s. The M75 grenade launcher in the M5 system had known reliability problems and was superceded in service technically in 1963 already by the redesigned M129. The rocket launcher was experimental and only carried a XM designation - it was a USAF aircraft rocket launcher adapted experimentally to a helo. How much of a success that was could be seen in what else carried that system, i.e. nothing - everything else used the M200. About the only weapon systems on the bird that weren't experimental - and were used otherwise - were the M18 gunpod and the M5 chin turret.
The ACH-47A was also comparably slow (well, not compared to a Huey), hard to maneuver with little loiter time, and presented a damn big target - three definite minus points for a gunship.
