Just adding to the Metalform recommendations. They are the standard by which everything else is judged, in my opinion. I had gotten out of the 9mm AR game in the mid-2000s, but came back in the mid-2010s. I stocked up Metalforms for my current gun.
Had a bunch of RRA-converted Uzi mags that worked pretty well. You lose the LRBHO but a properly-converted Uzi mag is usually a solid choice. Cheap Uzi mags are still out there, but will likely require some cleanup effort on top of cutting the catch.
I had a ton of bad experiences with the CProducts 9mm mags. I remember those were so hotly anticipated back when they first came out as a cheaper alternative to Metalform/Colt. And they suuuuuuuuuuuuuuucked. Then the CProducts legal drama llama showed up and the company flaked out on their initial efforts to "fix" them. Some folks had luck with them, but you had to get your mag block just right, or tweak the mag catch slot just right, or they misfed constantly. Sold the two I had for a song just to be rid of them. The current CProd mags are OEM for IWI's 9mm Tavors and Colt's 9mm ARs. Big endorsements I suppose, but I don't trust them after my early experience.
I tried a Promag, and it was terrible. I give them credit for stuff like the HK93 mags, but their Colt-style 9mm mags were straight up garbage. I think I ended up throwing it out.