So my absolute favorite assault rifle has always been the Ares Alpha. Integral smartlink, two points of inherent RC that stack with everything, big magazine and no suboptimal mods (laser sight, Gas Vent 2) that would go to waste. However, it's Legality F due to the grenade launcher. Even the Ares Bravo (which has a vibrobayonet instead of a 'nade launcher) and the Ares Sierra (which instead has an underbarrel stun baton) are Forbidden. Yes, even the rifle with a non-lethal secondary option is rated as Forbidden, while most assault rifles are only Restricted. The M22A3 and the FN SCAR-H3 battle rifle, which have grenade launchers, are also only Restricted. What the heck, guys?
So, with the Ares "NATO Phonetic Alphabet" series out, we have to look at the alternatives.
The AK-147 has a big magazine, a point of inherent recoil comp, and is cheap.
The M-23 has a bigger magazine and is almost as cheap. The fact that it doesn't come with any mods or accessories means that you can outfit it as you wish. The lack of any inherent recoil comp means that you'll max out at RC 7, tho.
(On a side note, never mount a Gas Vent 2. Gas Vent 3 only costs a little bit more and is superior.)
I'd recommend the Nitama Optimum II, but it's Forbidden, and once again I can't figure out why. It's got an underbarrel shotgun, not a grenade launcher.
The M22A3 I only recommend if you want to exploit a loophole in the legal system to have a grenade launcher that's Restricted. The less-lethal grenades are also only Restricted, so it could work.
Looking at the Onotari Punisher, I dig it. Don't let the fact that it's big in the Middle East discourage you: American weapons retailers import weapons from all over the world for interested gun enthusiasts. One point of apparently-inherent recoil comp, an imaging scope, and not too expensive. And I agree: it looks cool. Heck, I say go for it.
Whatever you go with, I recommend that you put the following on it as accessories: Gas Vent 3, Shock Pad, Foregrip or Underbarrel Weight, vision magnification for the scope (if you don't already have eyewear/eyeware for that). Combined with the Personalized Grip you're already planning to get as a mod, that will get you RC 6, or RC 7 if it's the Punisher or AK-147. The Heavy Barrel mod will add another point of RC, but it's 3 mod slots, so you may not have room for that with everything else you want. Getting a smartgun system installed is a must, of course, but don't forget to also get a Skinlink mod, as having your gun hacked is quite unpleasant.