I've had my Glock 17 for almost 12 years, must have put around 20,000+ rounds through it in that time. That being said, I recently bought an XD9SC for my everyday carry and its a great little gun. This is one of those "can't go wrong either way" decisions. The Glock has more history of reliability since its been out for so long, but so far, after 4,000 rounds, the XD hasn't given me any signs that its not as reliable as the G17, I'd trust my life to either one.
Go to
http://www.hs2000talk.com/ for more info on the XD or
http://glocktalk.com/ for more on the glock. You'llbe able to find pissing matches comparing these 2 fine guns on either site.
Glock +
Simpicity (fewer parts)
more compact (low bore axis)
Tenifer finish
Shorter trigger reset
Polygonal rifling (more accurate but can't shoot lead)
Biggest negative for me on the Glock is the Ergonomics. The grip angle is extremely raked compared to the XD. You can get used to it and adjust. Try this test...at the gunstore hold a Glock in your hand and gently squeeze into a comfortable grip, did the muzzle rise slightly? Even after 12 years it doesn't feel as natural for me as a 1911, CZ, Hi-Power, XD type rake.
Springfield XD +
Ergonomics (this is subjective, but the grip angle is closer to a 1911 and it points very natural for me. After shooting the XD I always heel and point high with the Glock, it takes a while to adjust)
Ambidextrious Mag release (I'm a lefty)
Backstrap Safety (some don't think its neccesary, but on a CCW gun a little extra saftey doesn't hurt)
Stainless drop-free Mags
Steel trigger group
Steel sights
Safer fieldstrip (the XD takes down like a Sig in that you have to lock open the slide (visual ID no round in the chamber) ,flip a lever, close the slide, pull the trigger...) Common sense would dictate checking the chamber before pulling the trigger on the Glock before fieldstripping, but there have been more than one AD reports linked to this very thing.
Biggest negative ofthe XD for me is that the brunel finish doesn't compare to Glock's Tenifer. Its also slightly larger and heavier than a comparably sized Glock.