I'll agree with Steve on this topic. I hada 26" barrel on my SX2 3 years ago--I did not shoot too well with it VS my SX2 in a 28". I was thinking 26" better for upland grouse---but it just did not do the job for me on waterfowl, so I sold it and bought another in 28". Many trap shooters use 32" barrels, the reason being a longer sight plane and follow through as I recall at the longer ranges. 30" used to be the norm in guns 70 years ago... but today 28" is the std.
Some mentioned the ballistics of no difference, I'll second that from my readings on the subject.
But here is 1 important factor--the shorter the barrel the louder it is. I was in pit blind goose hunting almost 2 years ago--a guy 10' away had a 24"-the loud concussion knocked me to my knees-and he was firing almost straight up.

Ears were ringing for days...

issed: There is no doubt about it- they are louder, a 26" is louder than a 28", but the 24" is just terrible for the report to the guys around you. I will not allow a 24" gun when hunting--I'll leave if I'm a guest before I'll knowingly subject myself to that punishment ever again.
Incidentely, there is a guy where I live that makes 4' barrels for guns---they hunt right next to houses and it make the report of a 22 short--very quiet. They use them for hunting urban crows and geese. In urban areas--the big factor is the new home owners calling the police because you are disturbing the peace-it may be legal to shoot there-but the police still will warn you one time-next time they issue you a misdemeanor for disturbing the peace when hunting with regular shotguns. So these "long guns" do the trick in keeping the neighbors happy.