ORIGINAL: Mite
The purpose for choosing a barrel length is mainly for gun balance. If you have a mod. choke in both 26" or 28" barrel, both will pattern the same. In clay shooting, more and more 30" barrels are being used. I don't know why. Heavier gun = less recoil?
Longer barrel because the farther the two sights are from eachother, the more accurate. PLus it may balance better for some. Personal preference.