Colt developed, and released an AR style 9mm carbine in the 1980s They used a straight steel 32 round magazine. The design was successful, and Colt makes a run of these occasionally.
A more recent development was a similar carbine in 9mm that uses a Glock pistol magazine. This appears like an AR, but originally the magazine release was not AR style, and they had no Last Round Bolt Hold Open,(the colt has always had identical AR controls, and operation just like a higher power AR). Recent Glock style ARs have fixed the mag release issue(now the release is in the same place as an AR), and a few Glock carbines have a LRBHO, but most still do not.
The decision which style you want to use.is yours. Both are reliable, both magazine styles are easy to find. I chose the Colt style. The 32 round Colt style magazines are cheaper than the 33 round Glock mags, but can usually only be found online.