I keep every choke in my bag. DIF, CYC, SK, IC, LM, M, IM, F.
I run IC most of the time especially in my 26" gun. If a small plate is far or small popper is heavy I switch to LM or even M. I'll run LM, M, IM or F for no shoot or difficult circus targets like stars at distance or spinners. Diffusion is great for any target 10 yards and in. Clays, big poppers and big plates can be hosed with a diffusion choke.
Shot I run 1145fps 1 1/8 oz 9 shot Winchester AA's or Remington STS for hoser targets. I run 1300 fps 1 1/8 oz 7.5 shot Winchester AA's or Remington STS for tougher targets. You vs make up for having less choke with heavier shot and/or more velocity. So having some high brass 6's or even the bunker busting 2 3/4", 3", or even the banned by NATO 3 1/2" federal Prairie Storm 4-6 shot load with the flight control wad in the bag can be handy if you ever want to disintegrate a spinner or take a piece of steel from 35-40 yards.
The best way to know what your barrel length, choke, ammo combo will do is to setup every possible target and shoot it at distance with every possible choke/load combo to see if it falls. The hardest target I've found is the mini popper. It takes quite a bit of pattern to knock that little guy down at distance.