Barrel length is a personal issue ...and I'm 6'5" and about 280 these days ( been on a big diet )
....and a short gun ( 26" barrels ) get too "whippy" in my hand ....so I tend to "yank" them around or "swat" at targets or birds vs shoot with a smooth follow-thru which is critical for sucessful wing shooting...
Some of my buddies like 26" barrels ...
For Trap guns ...I go to a heavier gun ( 10 lbs / and 32" barrels in an O/U ) because the targets have less left to right movement. Everything is more or less in front of you --- or off at a 45 degree angle. Heavier and longer on a Trap field - is a plus ( less recoil / gun stays in motion better on follow thru ) ...
For bird hunting ( pheasant, grouse, quail, etc ...) and sporting clays and skeet....I like an O/U at around 8 1/2 lbs and 30" barrels. A little quicker gun / more left to right movement -up and down, etc ... but not too light.
The 20ga SuperSport with 28" barrel only weighs 6.3 lbs / the 12ga with 30" barrel only weighs 7.3 lbs ...so they're both really light.
Picking a gun weight / and barrel length ....is up to you ...me, being a Buffalo ...I go a little longer and heavier. If I was 5'8" and 160 ...with shorter arms ...I might go to a 26" too ... but its all about finding that perfect balance between weight, length, balance point ...and "Fit" so the gun hits where you look ( there is no rear sight on a shotgun ) ....your eye is the rear sight / and the angle of the comb, drop at heel, etc all makes a big difference..to "Fit" ...
So for me --- a semi-auto shotgun is a compromise ( heavier guns recoil less / they absorb more recoil ) .../ and its kind of a one gun - does a lot of things pretty well kind of a gun for me ... But a semi-auto will never be a "primary" gun for me ...that'll always be an Over Under..
A semi-auto with a 28" barrel / is the same overall length as an O/U with 30" barrels ( because receiver is longer on a semi-auto / or a pump gun).
But there isn't a black and white ...do this / or do that ...you have to shoot them to get a feel for what fits and what you like. But a little longer / when its a lighter gun ...for most adult shooters ..is usually better than shorter.
Hope that makes a little sense ...( and if you don't have one / you need a good 1911 anyway ) ....call 1-800 - wilson combat ...and they'll fix you up