They have a slightly larger Range than Pistols, meaning that characters will find it easier to stay out of Boss AoE skills, or at least theyll have less distance to run to avoid them.
Rifles also have a higher damage output than Pistols. It is much easier to one-hit-kill a monster using a Rifle, especially in early gameplay. Their attacks are not weakened by any sort of armour, and they will penetrate a medium armor (eg Leather Armor) most efficiently.
There are only two stances for Rifles, Standing Shot and Kneeling Shot. The latter is rather useless in most siatuations as it renders the character completely immobile whilst attacking. You have to change stances just to move to another part of the map, which eats up time and gives mobs more of a chance to attack you. Standing Shot is however a solid stance, with useful skills.
Attack Speed is quite low in comparison to Pistols, and being a two handed weapon there is no room for any other weapon to be equipped.