When playing mods like exile where I need to find weapons more then likely an MX. Easy to get your hands on and sounds very satisfying.
When playing ALUK it would have to the MXC or Vermin. Most situations are up close so I need a close range weapon.
MX-M. Makes for easy shots close range or at distance, stick a bipod, DMS and maybe a suppressor and you've got yourself a sexy set up. Most mods the ammo is easy enough to find as well!