Deciding on the best barrel length, is mainly up to personal preference.
One of the biggest myths out there, is that a longer barrel will give you more range or improved accuracy. Both of these are not true. A longer barrel is just longer. It will not provide more accuracy or distance.
Most of the testing shows that a barrel needs to be around 8 inches in length to achieve the correct velocity without running very high pressures. Anything after 8 inches is all preference. There are however some drawbacks to getting a 8 inch or 26 inch barrel.
A very short barrel will make the gun a lot shorter and make you a smaller target. The smaller target however is from the side, and most of the time you will be getting shot at from the front making that small side profile not so important. Short barrels are also much louder than longer barrels. Many players also find aiming with short barrels much harder than with longer barrel, think rifle vs handgun.
There are a few advantages to longer barrels. They tend to be quieter, due to the added porting. The extra length also making sighting down the gun much easier, and target acquisition comes much more naturally. By longer I mean 12in to 16in. Getting a barrel longer that 16in, is just going to be LONG. Although like we said before is all up to you, the user.
Barrel length might not help with accuracy but paintballs sure will, getting good quality paintballs are a large portion of getting good accuracy. Check out our section on bore size for more on accuracy.