You need both, of course- but I think you are asking because you are shopping for a gun (marker, whatever).
Accuracy comes from skill at aiming (quickly). You can't buy it, though you can have three components of gear that will make it possible: a set of barrels with a range of bore sizes, a good regulator, and an anti-chop system of some kind (as a feature of your gun). PS- blowback markers buck like crazy, so shot to shot accuracy will be disappointing.
If you are playing tournaments, you need to be able to shoot at least 10 ball per second. Someone will argue this, no doubt, but dominating the opponent by volume is how you dictate the way the game unfolds.
Barrel to paint fit is important if you are using good paint. By good, I mean close to spherical, with very consistent size. If you are using crappy paint, go big on the bore and hope everyone is in the same boat.
A good regulator that keeps your velocity within a reasonable range will mean that balls follow the same arc. This is important particularly when shooting at opponents that are farther away.
Broken paint makes skill at aiming pretty useless. If there is poo in your barrel, you won't have very good accuracy beyond like 6 meters (look at the American using the metric system
). You want a marker that has a
cycling pressure that is super low, or better, a reliable anti-chop system integrated.
If I am misreading you about the whole shopping and trying to set priorities, you probably skipped most of this anyway, but my apologies for the verbosity.