As oldelkhunter has stated so well, barrel length does not affect choke. You didn' t say specifically what you were going to use the gun for. That would make a difference in what I picked. If your going to get serious about trap then (depending on your physical demensions) I would opt for a longer gun. By the way trap shooters prefer a tight pattern so your friends problem would be more a matter of technique and swing rather than a pattern issue. If skeet or sporting clays are something you want to get serious about I would not choose a pump gun to compete with. I have seen people use them well but they put themselves at a tremendous handicap in doing so.

For most hunting situations a 26 inch barrel would serve you well. As has been stated the differences in performance between a 26 and a 28 inch barrel are negligible. You need to go heft a few different guns and see what feels good to you. If possible shoot them. Things will get so much clearer for you then.