Paintballs

The best thing to do is check the paint to bore match with your barrel, you want the paintball to fill the bore to the point that it won't roll through on its own, but can be easily blown through by mouth. If it's too loose, it'll be inaccurate, if it's too tight, it'll break in the barrel. Also, since you're running a stock cyclone, I'd suggest something with a slightly thicker shell until you get some soft paddles for the feeder. The good news is that thicker shelled paintballs tend to be less expensive than thin-shelled tournament grade paint. The bad news is that it may take a few extra shots to ensure you get a "break" on target.

Marballizer, PMI Premium, Formula 13, DXS Bronze, all good stuff to use.

Then you can go for something with a bit more brittle shell that has a good paint to bore match. I'd stay away from the top-of-the-line stuff given the cost-benefit ratio. Stick with the mid-grade stuff and you'll do just fine.