I shoot O/U improved/modified. 12 ga with bl=26". Buy a gun for the bulk of your shooting.
20 ga work great too.

For trials and hunting we like the Federal Premium copper coated 6 with 1 1/8oz shot. It's fast and patterns great out of our guns.It's a great late season shell when the birds are getting up in the next zip code.Itcan thumpa bit but if you have to use the second shot then the bird is anchored and that's what it's all about.

PATTERN your chokes with a variety of shell choices. If you can't get your first choice then you know what your second choice will throw.
HAVE YOUR GUN CUT TO FIT it's worth every penny.