What you want in terms of barrel length is a suitable length to accelerate the ball and give you an aiming reference and balance the weight of the gun well, but not excessively long as to present itself as too much a target, waste gas, and be difficult to keep clean. Generally, the back (no porting, consistent bore) should be around 7-9 inches or so to provide the needed distance for the gas to push the ball up to speed. Anything after that is just for balance, quietness, and aiming reference. Some barrels are good at 10 inches, providing all that you need within that. Other times, a 14" barrel is wanted to provide better aiming and/or further acceleration distance for lower pressure guns the gas has a slower and steadier push that takes more distance. The middle ground is 12", which is short enough to stay close behind cover but long enough for balance and pointing. I personally specialize, having a set of 10" barrels and a set of 14", each suited for different paints and different positions on the field.
The sort of happy medium that most people go with to suit most paints and situations is a 12" .688 or .689 sized barrel. I would recommend DYE Xcel, CP, and BOA.