There are SOOO many variables. Simply moving to subsonic ammo for instance makes a big difference, size, I you don’t allow the slide to cycle etc. better question is what are you going to do with it. Are you storming the sands of Iwo Jima with it, or do you want the ability for multi caliber use, maybe full auto, is size or weight the most important?
For me, I chose the Yankee Hill R9.
1. Availability of a host of mounting options, I have a Tri-lug, 1/2x28, 5/8x24, and a nelson piston device.
2. multi caliber rated anything less than 9mm diameter, 223/556, 308, 300blk, 350 legend
3. Stainless fully welded (means its heavy compared to aluminum) and non disassemblable
4. the #3 items mean it is full auto rated, and you basically can not break it. Say if you drop your gun.
5. Price was right