All else being the same, these are the non-human factors in accuracy:
Crappy paint through any barrel and any gun will shoot like
Once you get high quality paint, get a decent barrel (if your gun doesn't already come with one). There are many, many, many, many, many different tests on accuracy, each one disproving another, so here is the round-about summery of what is most accurate:
Slight underbore or overbore is most accurate
bore matching is below that
significant underbore or overbore provide the worst results
Once you have a decent barrel or barrel kit, the gun is the last factor. Things like consistency, kick, etc, do have small effects on accuracy. However, having a decent gun or better, the differences will be so insignificantly small that the human element would cancel out any benefits.
Which leads to the biggest factor; you. Paintballs, even on the most accurate setup, you have to compensate for arch, movement, etc.