Personally I've tried 10" to 20" barrels and have noticed minimal if any difference in accuracy/efficiency from the 12"-16" range. Mind you my setup is stock. I run CO2 with a remote, no regs or expansion chambers. I get pretty much the same results shots per fill and accuracy from those barrels.

I do agree with the people on here that your playing style more than anything should dictate what barrel length you use. From what I've read/seen there isn't enough of a difference in "GOOD" barrels to say that one length is better than the other. I use a shorter 10" barrel for the simple fact that I play alot of urban/cqb matches and a longer barrel is more of a target than anything when I'm trying to clear rooms and shoot from limited cover. But like I said, thats just my style of playing. Just my $.02