I've got an XDm in 40, main reason for picking it over the Glock is I'm not a Glock fan. Yes they are bullet proof reliable, made by the millions (reason #1 for not liking), used in every gangster movie (reason #2), our range has about 500 of them (reason #3), they look too, I don't know, plain (reason #4).
I've got a friend with a new Glock 40, very nice shooter.
Our resident pistol expert has fired both and feels he gets more accuracy out of the XDm.
In all honesty it comes down to preference, both are excellent and very similar. I went with the XDm in part because it's rare, got one of the first shipment of 20 Sask GW brought into the country. Everyone at the range wants to try when they see it, while my buddies new Glock sits there with 10 other's on the table.