Carbine as in statistics and price, would be considered the best. It has the most damage of any other automatic-fire weapon other than the A12 at a lower fire-rate. Saying that, it has a modest fire-rate, and almost no recoil. In that all you have to do is hold down the mouse, which requires little skill.
G36 is my personal favorite of these guns. It has the same damage as the starter pistol (USP). But has a fast fire-rate similar to that of the UMP-40. It has high zoom which is ideal for aim. Although it does have higher recoil which can be dificult for newer players.
Vector X is one of the best automatice-fire weapons, with both damage and fire-rate on its side. The recoil is more than that of Carbine but lesser than G36. It has a fast-fire rate and high damage. The only issue with this weapon is that it does not contain enough bullets per magazine or in reserve.
All 3 of these weapons are based upon your play style. If you prefer an easier to control weapon with high damage, you should get Carbine. If you enjoy firing from a distance and fast-firing guns, I would suggest you get G36. Or If you prefer aspects of each weapon combined get Vector X.
Note: None of these weapons can truly be better than the other. (Unless it is in statistics). It is soley on the player and how the player uses each weapon.
I've done my part of the research on this, and made a video (by that time Max hadn't added quantitative stats of weapons, so i had to record by myself, which is a little less accurate from the original stats, but in comparison, it will give you the right idea).
Here's the AR guide a year ago: https://www.youtube.com/watch?v=vLtkpH-fYus&t=93s&ab_channel=Nisar
In summary, I'll agree with Fallen . But personally, when Vector X arrived and I compared the stats with other assult rifles, I concluded that Vector X is the best assult rifle of this game. It has the highest fire rate, lowest recoil, and a moderate bullet spread. And among other assult rifles, it has ability the kill the enemy in lowest possible time, whether you go for head, torso or limb. It has the recoil and Fire rate of SMG's and damage capability of AR's.
