Whichever one hits where you point it - and you won't know until you put it on paper with both slugs and shot (assuming your short barrel is actually IC). IC is not the same as a Cylinder choke - the latter having no constriction.

An IC choke is fine with premium ammo (better Trap/Sporting Clays loads in 7.5); not so good with promo/dove loads, where you need at least LM to compensate for soft/regular shot.

After you shoot a match or two you will be more able to make an informed decision.

I prefer around 21" with a vent rib, which can also get by on a clays field. For Sporting Clays - the ultimate in movers - it's 28" minimum for a smooth swing.