ive owned an XD-SC, XD service 4", G27, and G19...
in my opinion XDs are MUCH more shootable, ergonomic, just plain easy to shoot, etc, etc. Your finger sticks to the trigger better and it seems to just come straight back with ease as you pull it. The glock trigger is at such a forward angle that just doesnt feel like you have much trigger control when shooting it. The trigger on the Glock can be decent at best with a lighter trigger connector at around 3.5-4lbs. The trigger still feels sloppy, cheap, and sharp compared to the XD in my opinion....even with the aftermarket glock "smooth style" trigger, the trigger safety still makes it uncomfortable. Springfield's trigger is much better, ergonimically speaking.
since i believe practical accuracy is a result from good ergonomics and shooting technique, the XD has the edge over the Glock. I don't bench test my guns, but thats because i only care how they perform in my hand, not in a rest.
The Glock does have the sleeker and smaller overall bulk to it.. it just feels smaller and more concealable, even though it is a bit longer. Also, the barrel on the G26/27 size glock is longer than the XD-SC, so you could squeeze some extra velocity out of your ammo. It also feels simpler than the XD, but the XD's features like the grip safety,loaded chamber indicator, and light rail(althought rarely used on the SC models) are still pretty cool if you ask me.
Go with whatever you like better. Both are good guns. I personally would go with whatever i can shoot better and what feels better in my hand if i could only have 1 gun. For me that's the XD..but since i own both, i find myself carrying my G27 because of its less bulky/edgy design alot of the time
I'm getting rid of both though to get a SIG P239 SAS w/ crimson trace lasergrips in .357sig and SA/DA...I'd take that over both the G26 AND the XD-SC.