I like most of them to be honest... But if i HAD to pick a favorite, i'd say the MR-28.
Its reminds me of the FAL OSW from Black Ops 2- those who have a quick trigger finger will completely dominate- unlike the MK14, IA-2 and the abominable SVU, which have a small firecap. I use Muzzle Brake- to get the most out of its good damage, and i swap between Red Dot Sight, for matches in Tremor or Overlord, and Thermal Scope, for matches in Stormfront or Stonehaven.
I also use the MK14, mostly cause i loved it in MW3. I use the standard Red Dot, along with Suppressor.
I like the SV-**GETS TOMAHAWKED**
SVU is my favorite. Its brutal with this class:
SVU @ Silencer/AP Rounds
P226 @ Silencer
Ready Up, Quickdraw, Incog, Focus
The bane of snipers on Stonehaven or any map with long sights like Stormfront. This gun is always a 2-shot, but can 1 shot headshot at around 30 meters if I remember correctly. This marksman rifle will also teach you not to exercise your trigger finger blindly, just be sure to double tap the trigger with accuracy for XP.