I've owned a 9mm AR carbine and pistol that were both built off of a CMMG dedicated 9mm AR lower and currently have a 9mm AR pistol built off of a CQ10 9mm lower. All three use the 32 round Colt stick magazines. There are 10 round Colt clone magazines available and the three I have seem to work reliably. My current one is running a 8.5" barrel and have no issues with reliability running factory and reman 9mm ammo. It is a great platform but be prepared to run through a lot of ammo. Biggest pain is loading the Colt magazines. If you go that route, plan on a purchasing a Lula loader. I've had mixed results running modified Uzi magazines and stick with Colt or Metalform for reliability.

My brother has built a few 9mm AR that use the Glock magazine and my experience is they are quality builds as well. Just as reliable as mine and I don't see an inherent advantage of one over the other. Outside of the magazine and mag well dimensions, there is little difference between them.

As my fellow Marine stated, it really boils down to magazines. Glock platform definitely gets the edge on magazine availability and you can at least get the 15 rounds magazines just about anywhere in CO. 10 round Colt pattern magazines are strictly a mail order option in my experience.