Hu's- Decent rate of fire, great damage after built in enhancements, 3 slots for enhanced damage mods, +3 to rapid fire. You can equip two of them. Not my personal preference because the range isnt what I'd like and 1handed guns degrade to fast for me.
Nikola- with 7 or 8 slots, you can stock it with some shield penetration, enhanced damage mods, or phase attack strength mods. It deals both electric and spectral damage and has a built in shock and phase value. Decent range, decent rate of fire.
Dunbar- Decent slot availability, look at all those novas! This thing procs novas like a beast with all different types of damage. It also deals all types of damage, and theoretically could be set up to add your favorite SFX at a decent rate.
Lee's- With 1 mod this thing can have 100% shield penetration. Great range for a rifle, INSANE rate of fire. Deals fire damage with ignite attack strength built in. Decent damage as well, especially for its rate of fire. +3 to beacon. This is my personal favorite if it has 6 slots. Throw a shield pen/ignite relic in it, one more high ignite mod and fill the other 4 slots with blessed mods and you've got a steamroller.
Voodoo- I'm not much for sniper rifles so I've never tested this one. I know it ignites which is nifty for a sniper rifle to have stock. Not too familiar with its other mods.