9mm is really the best caliber, some say light 40cal are equal in kick and power.
The true best round is the wildcat 9mm (9mmX25mm...) they are usually more than the 9mmX19mm ammo usually ranging up to 9X25mm this gives you a flatter shot and is more accurat while still using the tried and true cheap 9mm bullet, butttt! u more than likely will have to handload these yourself, unless u are lucky enought to find someone who loads and sells them, this is the best round to shoot and the top pros shoot them, but the normal 9 will do fine too, and if not into reloading is the ideal round to shoot.
*If u dont alrady have them i would reccoment adjustable sights and a dual action recoil spring!
www.efkfiredragon.com has the spring for about $60.
As u know ported barrels are prohibited and reduce recoil about 25%, but the recoil springs are allowed and reduce up to 40%!!!!! Wich is like going form a 357mag to 9mm and will get you follow up shots on target much quicker.
IF U HAPPENT TO OWN A 1911 THE 38 SUPER IS GREAT, AND I HAVE ALSO HEARD GOOD THINGS ABOUT THE 400 CORBON!!
The cheapest way to reduce/absoarb recoil is to buy a hogue rubber wrap around grip for $12 bucks, this helps greatly and feels great, and is cheap.