I have been a Springfield xd fan and owner for 4 years. Recently looking at getting a new firearm an have been drawn to the G21 gen 4 or sf. I know alot of good and bad on both firearms. Currently I carry a Springfield xd 40 subcompact as an everyday carry. I have been wanting something not to replace my everyday carry but to have for home protection and just play around with. I know Glock is a superb firearm and have shot a few in various calibers. My questions is this. Caliber of choice? And model of choice? Remember I am a Springfield fan.