15 years ago
The flatline barrel should be your best bet. It produces back spin on the ball making it stay on a path. Try upgrading your paint. Cheap paint or paint you buy from wal mart won't be the roundest because its cheap paint. Spend 40 bucks on a case of balls from the internet and I guarantee you will have better performance.
Also check your velocity if it is cranked to high your balls will go wild.
Now to answer your question. The best barrel on the market is I say the Freak. The freak system allows you to select a size for the individual bore size of your paint you are using. You basically measure your paint and then find the right insert to use.
But the down side of this is the freak system cost about 150 bucks.
But try checking your velocity and use a decent paint quality. The flatline is a good barrel. Also now that I think about it, make sure it is properly fitted on your gun. Make sure it is on right.