KSC G19 all the way, hands down. Get a metal slide on it and the weight will impress you! Literally feels like a real steel Glock. The frame is metalized ABS Or polymer of some sort which is very solid and heavy. The G17 is more toylike, ABS frame that really sucks.
And, the only differences between different Glocks is the caliber, the height and length. So any holster made for a Glock will fit any Glock out there.