One thing the XD is superior to the Glock in is handle diameter and that's only for people with short fingers. That's it. Even that is suspect now that Glock has introduced the SF frame model. Other reasons given to the XD's superiority are subjective to opinion and nothing else.
A few of the given "reasons" XDs are better I've read:
Price.
The Glock is about $80 more than the XD. I don't know many people who think $80 is something to worry about with something that protects your life. I just put $80 worth of gas in my truck this morning.
Machining quality/manufacture.
I have seen XDs go out for warranty work, (sometimes complete replacement due to inability to repair). Cracked frames, ftf, stovepiping, chambers needing to be honed. The list goes on and on.
Durability.
Like the aforementioned reason - it's false. Most people have this opinion based on only having a few thousand (if that) rounds through their XDs. At the indoor range I shoot at they are constantly having problems with their XD rentals, (see previous reason problems), while Glocks usually run about 100,000 rounds through them before they cycle a new one into the mix. Those are 100,000 trouble free rounds. Consistently. Wait a few more years when all of these XDs get some real use.
Ergonomics.
XD likes to tout this one in their advertising as well saying that when you point it the sights line up rather than having you look at the top of the slide. Glock went with their 105 degree handle angle for a reason: they tested, tested and did some more testing and found that it provided the best firing results for accuracy and following shots. The XD's handle angle along with its high barrel axis to the hand provide much more muzzle flip than a Glock which in turn means less accurate double-taps and a less control.
Single action vs double action.
The Glock uses the double action for safety. It's one of the reasons it's called Safe-Action. If the striker spring isn't cocked - it can't fire! Just like a down hammer. The XD has a cocked spring. You can count on replacing the striker spring many more times in an XD than a Glock because of this. You also better hope your firing pin block is in proper working order or you're at the mercy of the poorly designed sear of the XD which, by the way, will fire out of battery. Try pushing back on the slide sometime while pulling the trigger. The double action might not be as smooth, clean or as short a pull of the single action, but these are service pistols not target pistols.
The slide lock.
The slide lock on the Glock is designed to be tight against the frame and slide as to not be snagged on anything. They also wanted people to use two hands to release the slide because it's a more controlled manner than hitting the lock with your thumb. This isn't the movies! Release the slide the proper way. The slide lock on the XD also adds a decent amount to the overall width of the weapon - not very carry friendly.
Finish.
Tenifer is not the outside coating. Tenifer is the metal treatment of the slide and barrel itself. It is .005 mm thick and is close the the hardness of diamond. The treatment of the metal itself achieves a 99.9% salt water resistance. Tenifer is also illegal in this country because the EPA. XD does not have it. Don't regularly oil the slide on your XD and carry it in a cold climate for a while. The in/out condensation will rust your slide in no time.
Warranty.
Good thing Springfield has you covered here, you're going to need it. Especially when you find out Springfield won’t sell parts to the public.
Field stripping.
The Glock actually uses a faster process which uses less steps than the XD. Also, many people rotate the take-down lever then pull the slide lock down putting all forward inertia of the slide to come to a halt against the sear (it's the only thing keeping the slide from going forward at that point) and cause damage to the sear, striker and frame.
Loaded chamber indicator.
Glock has this as well.
Cocked indicator.
Glock has this as well. If the trigger is forward on a Glock, it's cocked. Also, how are you going to get a round into the chamber on either of these guns without it being cocked? It's not a Walther with a decocker.
Grip safety.
How is a gun going to go off without your hand on the handle? Your finger should never be inside the trigger guard unless you have the weapon acquired and intend to fire. Are we forgetting some basic firearm rules? The grip safety is null and void.
Customization.
If you can't find genuine Glock custom parts for your Glock at your local gun dealer, you need to find a new one. Glock holsters, parts and accessories are everywhere. Try to find a holster for your XD. It's much more difficult. Yes, it's newer and takes a while, but companies will be reluctant to make them because Springfield supplies you with one, albeit a horrible one with not one level of retention.
I felt the need to debunk these XD/Glock myths. The XD is not even close the being up to par with the Glock. The Glock is going on over 20 years now, and has changed the world of pistols - the XD won't make that sort of impact. Bill T.