I usually roam around carrying a MK17 and a SR645. Although belt fed weapons are great fun for messing around with. I like the M1891 for really long range work, no silencers available for it but so long as the nearest enemy is greater than 100yds it's not a problem.
The SASG is nice for those rebel missions where you have to breach those large buildings and hack the computer.
I also have only unlocked about half the weapons and mods in the game. So I cannot say for sure which is the best of the bunch.
