12 to 14" is all you need unless you'll be doing some tournament stuff and then the 16 can come in handy for pushing in the sides of the blowup dolls so you can stay more in cover while shooting out of the indent you made.
Odd and unpopular though it sounds if you shoot decent middle grade paint from a recognized brand and from fresh stock the stock barrel will shoot as nice as anything else. I've shot my stock pilot with the stock barrel, a CP barrel and a Lapco barrel and they all shot very close to the same with the Lapco having maybe a very slight advantage. Or I may have been holding the gun a little steadier. Bottom line is that all three barrels were able to put my decent quality paint into an dinner plate sized spot about 70 to 80 feet from me. And that's about as good as you can expect from paintball.
I had a "Paintball God" moment once.
Like Al Bundy's Polk High football moment I live on
for the slim chance of repeating that one time
miracle in some small way.........