Hi, welcome to H&G newcomer. I'll be your guide.
As an introduction, let me tell you about heavy set first.
The shots to kill against no-heavy set are irrelevant, as most people run the badge silver minimum.
Arguments about a weapon's damage is based on it's hits-to-kill against heavy set gold and silver, usually gold. Not against no heavy set.
When it comes to heavy set silver and gold, neither AVS, STG nor M2 will 3hk stock bullet. The only one of them that can 3hk heavy set silver and gold is the AVS with a bullet mod, which gives a lot more recoil than a bullet mod on the STG/M2. Most people don't run bullet on their avs.
Meaning, all of the ARs will in most cases be the same amount of hits to kill apart from bullet-AVS.
This is completely wrong in every single way. Straight up lie you came up with on the spot.
In cqc, it is irrelevant whether either the M2 or STG has a bullet mod; they will be the same hits-to-kill against heavy set silver and gold.
What it then comes down to is the rate of fire (ROF); where as the M2 has the same rate of fire stock as the STG and AVS has with both a trigger and spring.
That makes the M2 the cheapest one of the 3 to use in CQC. If you decide to put the trigger and spring on the M2, it will heavily outperform both the STG and AVS (granted no AVS bullet) in CQC for the same repair cost as the other two.
Any skilled player knows this is the case, and that is why skilled players don't argue against the M2 being the strongest; everybody knows it is the strongest CQC. They argue that it isn't as viable on range.
Listen, I'm not trying to pick at you personally. There just comes a day for every new player when they need to be put in their right spot about weapon statistics.