Have been following this thread with some interest as I know some of the fellas that have posted here and respect there opinions. I haven't shot with any regularity for a number of years but there was a ten year period where I averaged 10K rounds per year, and one year close to 14K. I shot on a competitive level for a while but work constraints stopped that for the most part. So I think I am qualified to make comment.
Longer barreled OU's were just starting to come into vogue as I was fading out of the sport. My shooting partner at the time loved Citori's and changed them like his under wear regularly, so I got to try the latest and greatest that Browning had to offer. I could just never get that warm fuzzy feeling over a 30"++ barrel. Why because it threw off my timing and hold points as it swung different.
The point of the whole game besides having a lot of fun is to grind up targets on a consistent basis. At the time 25 on a skeet field for me was common, and I could hold my head up well on any sporting clay field. So from my perspective at the time why would I deviate from my 26" & 28" barrels which I shot well with. I always shot a Winchester 101 with 26" barrels, and my 410 had 28". I later bought a Classic Double's skeet version with 27.5". Which is basically a Win. 101 with all the bells and whistles on it. My issues with taking my shooting to next level did not lie with gun mechanic's and barrel length, but were purely psychological. The mental game in this sport is huge, far greater than most fellas realize. My mentor and advisor on these matters in my early years was chap from the USA that was well known, and world champion in 28ga for several years. For some reason he took a liking to me and gave me a lot very good tutoring and advice.
Having a gun that "fits" you and your comfortable with is of the upmost importance. If your just learning the game pick a barrel length your comfortable with, doesn't matter if it's 18" or 36", if it's attached to a gun that fits you and your grinding up targets consistently at all stations with then that's "your" gun. Don't be swapping guns every 6 months, once you find the one stick with it and, practice, and lots of it will give you the technical aspects, sight pictures etc. your body will eventually develop the muscle memory, all the while tackling the mental aspect and do not ignore this part of it. Then there's raw talent. As most hockey players will never play in the NHL most shooters are never going to be in the big leagues either. The main thing is to have fun.