If you are planning to use it at all for personal protection, I would recommend the G22 or G35. Either would give you 15 rounds of 40 S&W ammo. The "40" packs more punch than the 9mm - larger diameter hole, heavier bullet.
Many people try to get away with the smallest caliber cartridge that might get the job done. Others, however, recommend carrying the largest gun (largest caliber) that they can effectively handle.
If you remember the reasons why the 45 ACP was developed, it was because the 38's that were issued to the military prior to the 45 were ineffective against the Phillipine insurgents, who would get high on some "jungle juice concoction" and wrap themselves in protective layers, and still kill our officers. The 45 ACP did what the 38's couldn't do - it stopped the attackers and has continued to do so ever since it was first issued. You have probably noticed that numerous of our military Special Forces units have re-adopted or have continued to select pistols in 45 ACP to carry with them on their assignments. There must be a reason for that.
Of course, some folks will propose that a smaller bullet traveling at a higher velocity is more effective than a larger one traveling at a slower velocity. Both philosophies have their supporters. I guess you should ask yourself how "small" you want to go. However, the 9mm is not a particularly fast round.
After all that................I own all four models, G17, G22, G35, and G21, so I have all the calibers covered. Which would (do) I carry? If it is my butt on the line, I will have either the 22 (40) or 21 (45) with me. I LOOOOOOOOOOOOOVE shooting the 17 (and my M92, too), but prefer something bigger when I have the choice.
Just my two cents.
S4F
NRA Benefactor Member
NRA Certified Firearms Instructor
NRA Range Safety Officer