Ive completed the M4A1, SCAR-H, UMP45, RPD, & AUG HBAR and have the titles for them. ACR though is my new favorite.. Im having a great time with this gun especially when paired with stopping power pro.
Also, Hardcore: HQ Pro is the best XP gameplay out there. I consistently get 10,000+ XP per match. All you gotta do is haul ass to the HQ each time its available to cap, and bust your ass to either cap it or destroy it. You earn XP for each millimeter of progress on the bar (for capping\\destroying) it seems. Lots of fun, lots of XP.