Decide what you want it for, clays, rough shooting, crows, bunnies, pigeons etc.
In its simplest:
clay guns tend to have slightly heaver, slightly longer barrels,32", not always good for a day walking round fields.
'sporters' tend to be a bit lighter with shorter barrels 26" - 28" good for a day walking round fields
semi autos - great for pigeons, rabbits, crows etc, good field gun
I dont want to get in to anything about whether over and under or side by side is the best, ita all a bit of a muchness really.
semi-autos on a clay or game shoot gets frowned on as its deemed n