These guys have pretty much nailed it.
Only other significant factor is in trap you can shoot 16 yd singles, 16 yd doubles, and handicap as far back as 27 yd. And the bird is always going away from you so a mod, IM or Full choke is best. 30 or 32, 34 inch barrels are best. As single shot is fine except of course for doubles
On skeet your birds are going away, approaching, and crossing, so a open choke, SK, Cyl etc and shorter barrel like 26inch is best. And a O/U is preferred to semi.
On Sporting clays the layout could be anything, so a double barrel with several chokes works best.