In NV, N. CA, and now FL, I use SK/IC to start with for Sporting Clays - an IC choke will break targets out to 40-45 yards very nicely. If I feel the need for more choke, I might use a LM or M.
To the OP - if you have fixed chokes, you will need someone to properly thread the barrel for chokes - you just can't buy some and screw them in otherwise. Briley does a good job, or you might even be cheaper buying an aftermarket barrel for your gun already threaded for choke tubes