Most of the people that I know,that still compete,are using the 40S&W in one form or another. Personally I hate the chambering and don't desire to own one.
Back in my day there were a lot of 38Super guns used. Today,that would be too expensive. I would most likely go with the 9mm. And most likely in the form of a Glock 17 or 34.
Why . . ? . . never fails,always goes bang,tons of aftermarket parts,easy to load for,cheap mags,super easy to do a F&B on (just to make sure).
Good luck and remember - - -> #1 is having fun. --- SAWMAN