Indeed the tippman's main advantage is the flatline, do not get it unless you are prepared to get the right paint for it, to set the FPS right and to clean it out a lot.
I have the Smart parts teardrop barrel on my and I found it to be very good, not to expensive either. I have also tried the Smart parts 21'' Tactical barrel, but that was just too long. I have also had the apex, again it is hard on paint but expensive for what it does.
J&J Ceramic or Palmers Brass are apparently the best to get. They shoot anything.