Between the two the Glock has better aftermarket support, spare parts are readily available, and it has a proven track record. The only fault I can find in the XD series, now that they're using a much improved finish, is a lack of common spares being available. Unless things have changed that I'm unaware of, any small part breaks (rare occurence) and you're stuck waiting on factory service, whereas there are tons of Glock armorers with spares who can have you back up and running quickly.
After that it's personal preference. I prefer the trigger feel and grip angle on the XDs. Both are fine pistols. Which one fits you best is the one thats best for you.