For guns, LMGs can typically do a lot and dipping into all kit weapons is more of a move for like, super tight CQB maps. I can’t say anything about which LMGs do the best performance wise but I can say bipods, a mid range optic, and big mags are essential on long range maps while the mag fed machine guns can be used more as an automatic rifleman/heavy assault rifle situation

For one, using LMGs to pin the enemy team is the best tactic to use, although, I'd use bipods, a hybrid sight, and huge magazines for long range maps. And on close range, use a RDS site with iron sights. I mainly use carbines with my Support class, you get the firepower of a assault rifle, with the speed of an SMG or PDW. For equipment, Ammo box and mortar or ballistic shield.