I currently have a G17 (9mm), but am looking into an additional G21SF. Yep, I'm one of those with the girly hands (guess I took after my 4' 10" momma). I've just read too much where the 9mm doesn't seem to have the knock-down power high enough to suit me. After all, the guy at Ft. Hood was shot 4 times with a 9mm (supposedly), and he's still alive. I know shot placement is a huge issue, but I don't want to have to be fighting adrenaline and an intruder and wind up not being spot-on.
Anyway, if I do get one, I plan to shoot a few rounds every now and then with the G21SF, but do most of my practicing with the G17 to keep cost down.
BTW, I've done the research, and the following are supposedly the best personal defense rounds there are, in order:
1. .357 Mag (based on 96% one-shot-stop)
2. .40 S&W (based on 96% one-shot-stop)
3. .45 ACP (based on 94% one-shot-stop)
So, why go with the G21SF (.45 ACP) instead of a .40 cal or .357 Mag? Because I can go direct to Glock and get the gun of my choice for the LE cost (I'm retired military). Saves me about $150. The G21SF just may be the one gun with one of the above calibers that fits my tiny hand.
Bottom line: Keep the G19 and get the G21 or G21SF to suit.
Just my $0.02.
Jonny