Im currently using the ACR which is the best HC assault rifle. It's minimum damage is 30 so its always 1 hit kill no matter how far the enemy is, only other weapons to have this ability are snipers, LMGs, and the MK14. I use impact on it so enemies behind cover are taken out easily. For attachment I switch between silencer if im playing more agressive, and ACOG or hybrid sight if im feeling more campy.
My secondary is an MP9, I rarely pull it out and use it just for its 75% sprint bonus.
Leathal: Claymore, Tactical: Smoke.
Perks: Extreme conditioning, Assassin, Dead Silence.
I only play hardcore search and destroy so my setup is best for that game mode. If i am playing something else or dont feel like going try hard I change the ACR for a SPAS-12 or AA-12 with range.
ACR w/ kick and silencer
Dead Silence/ sitrep pro (sitrep is really nooby now, so I would avoid using it, unless you don't mind the hatemail, lolz)
Support packae- UAV and Ballistic vests, nothing else.
That is my best/favorite class and I gurantee that you'll like it.
Any gun with Silencer
-On HC, most players use Blind Eye so its best to use KS that you can control.
-On Smaller Maps like Dome and Hardhat, Recon is so wonderful.
-Be aware of Ballistic Vest on HC. Just keep shooting until they are dead. Don't just assume 2 bullets and run away.
-Always be moving! Campers will get eaten by Noobtubes. With dead silence on, you will sneak up on quite a few campers and get easy kills.