Can't really go wrong with the Honey Badger (grip + extended mags) on smaller maps, or the SC-2010 on bigger maps (any combo of attachments, it certainly doesn't need a grip)
For perks, the best "spine" you could build your loadout around is probably stalker, dead silence, amplify and focus. Add scavenger or fully loaded if you're using kill streaks, or another two point perk if you're using specialist. Sleight of hand, ping, hardline, agility/marathon or even ready up + takedown work well here.
Keep two variants of this loadout with the above core perks, only with blast shield and blind eye in the last slot for each. IEDs and trolls are everywhere so a good CQB gun (Honey Badger is in my blast shield class) and those perks combine for a strong counter class. For blind eye, aerial kill streaks are more deadly on larger, open maps so you may be tempted to go with something like an R5. But the SC2010 is more accurate and kills faster at range anyway. Plus, oracles and sentry guns are a threat on small maps too, and the SC does better than an R5 up close, so go with the SC.
For SMGs, you can't really do better than the MTAR (suppressor/muzzle brake + grip) or the Bizon (same attachments, or grip + ext mags). The Ripper isn't good as a "proper" SMG thanks to mobility issues, and it has the worst range of ALL SMGs. The MTAR has consistent damage, whereas the Bizon has fire rate, so go with whatever suits you.
Go with ready up, steady aim, dead silence, amplify, focus, and then scavenger/fully loaded for streaks, or sleight of hand/hardline/agility/marathon/ping if you're using specialist. You may wanna setup an SMG blast shield class too; just put BS in as your last perk.
For other AR classes, the R5, AK and FAD are solid choices. But at the end of the day, it's not the gun that does the pubstomping; it's the player. These classes won't turn you into a good player until you've got map knowledge, reactions, aim and all the rest of it down. But I know from experience that the above classes are great when you use them in the right situation.