In my possesion I have all kinds of barrels, short, long, ported, unported, rifled and whatever else there is. (ramrod LOL)
I personally have found that some short barrels shoot a lower velocity than when I put on a longer barrel with the same inside ID.
I guess this would be due to the wasted gas syndrom. A longer barrel lets the ball take full advantage of the expanding gases. (especially liquid Co2)
However, my favorite barrel, in my humble opinion, is my 14" bushmaster SI barrel. No bells, whistles, just smoooooth. And in the same breath my 18" bushmaster barrel is the worst.