You probably want to consider a 40 cal model. 9mm will limit you to minor class which is usually not in your best advantage.
Aside from that there's not a huge difference between the suitability of the different models. Sure, there's a slight sight radius/weight/stability advantage to the longer models but its not typically the kind of margin that you win or loose on. If you are competeing at the level where those margins do make a difference you will have already bought, worn out, replaced, and upgraded half a dozzen guns and fired a quantity of ammo with a value 10 times what you've spent on guns.
If I were you I'd get a Police Trade-In/Factory Refurb G22. With the money you'll save over buying new, you can buy a Dillon Square Deal reloader. Access to more/cheeper practice ammo will make more difference in your competetiveness than an inch of barrel ever will.