There isn't a "best" barrel for any marker, it's whatever you can afford, and whatever is available in the threads that your marker accepts.
Most common threads right now:
- Autococker (after the WGP Autococker, which isn't actually one of the oldest markers, but it is considered the first serious tournament marker)
- Tippmann (A5 threads & 98 Custom threads).
- Spyder (spyders use them, of course, but so do all spyder clones).
- Gog/Smart Parts (also referred to as Ion/Impulse/NXT, after the markers most associated with those threads).
Most common barrels right now:
- CP (Custom Products)
- J&J (specifically, their J&J Ceramic)
- Freak (a barrel kit that uses inserts; made by Gog, formerly Smart Parts)
- Dye Ultralite (really only because they come stock on Dye markers)
- Deadlywind Fibur (carbon fiber barrel that uses Freak inserts)