Smart Parts Progressive
32 Degree Quiet Riot
10.5" Unported Brass Barrel
Anything of decent quality. Draxxus Hellfire worked pretty well.
I've used a fair amount of aftermarket barrels and nothing compares to the brass barrel. With all of my other barrels, some paint works great, other paint doesn't. With the brass barrel, it shoots basically all types of paint equally well. Even when my other barrels are perfectly matched to the paint, they don't shoot as accurately as the brass barrel.
The brass provides less friction against the shell of a paintball so it requires less force to propel the paintball. That means you use less gas per shot. Also, the nice golden color of the brass is both a strength and weakness. It's a strength because people off the field are always commenting on it. It's unusual and makes you feel like you have something special (which you do). However, in some situations it stands out a little bit and can give you away in the woods.
Some Brasso on the barrel every so often and it's good to go.
It's the most accurate barrel I've ever used. It shoots all paint very well. I recommend them to anyone.