SIG makes a fine, quality pistol. No argument. But the pistols ain't small. The P220 Compact, with 6+1 capacity, is 7.8 inches long, 5 inches tall, 1.5" wide, and just over 31 ounces with an empty mag. That's a pretty hefty pistol for the 6+1 .45 ACP you get in return. Too, I (just me personally) have never been a big fan of DA/SA (manual decocking) pistols only because the operator must be competent with two very different trigger pulls on the same gun.
I have no data, but I'll bet lunch money that the P220 Compact is inherently more accurate than the G30. That given, the Glock is smaller in all dimensions--it's even thinner and lighter--and it carries 10+1. 'Course, you put 11 rounds in the Glock and seven in the SIG, and they may weigh about the same (dry, the SIG is about six ounces heavier).
The big thing: If you haven't shot both pistols, don't make up your mind until you do. Range rental, borrow from a friend, whatever it takes. One pistol may instantly feel better in your hand and feel like a natural point of aim. That may outweigh any stats about size and capacity.
Good luck!
P.S.: I like your choice of caliber. Not to start THAT caliber-preference dead horse kickin' again. I just, personally, like .45 ACP as a carry round. I hope Ranger SXT +P (RA45TP) can be found somewhere again soon...