My opinion on Weapons in this game:
Pistols: Backup weapon or if you only have 1 hand to work with. [fast, good accuracy at short ranges, good reaction shots]
Machine Pistols: Prinary weapon when you only have one hand free. (eg shield) [sligtly worse stats reaction and accuracy wise than pistols but with burst and full auto capability]
Sub Machine Guns and CCQ Carbines: Used for agile maneuvering, quick movement, good firepower over short ranges.
(Assault) Rifles: Good accuracy and damage over all ranges. no reaction shots except set on overwatch
Marksman Rifles: Good accuracy at medium and long ranges. bad accuracy at close ranges. only overwatch reaction shots.
LMG: good suppressive capabilities. accurate when deployed (shooting over barrier or prone) spray and pray when fired from the hip.