We just went through this selection at my department and evaluated numerous manufacturers rounds. Our requirement was reliability, stopping performance, and body armor penetration. The ability to defeat body armor was the main consideration is getting our rifles, 2 Colt M-4 select fire(14.5"bbl), and 2 Colt Commando's (10"bbl) select fire. Maximum deployment range was determined to be 80 to 100 yds, anything further would be handled by our G-3's or bolt guns.
Using the above criteria, my Department selected XM-193 and Q3131a as the specified ammo. It has reliable stopping performance out of both weapons, there are no reliability issues with this mil-spec ammo in these ex-military weapons, and both rounds were capable of defeating body armor at the ranges specified. Another factor in selecting the 55 gr round was if other milsurplus weapons were obtained for issuance as a patrol rifle, there would not be a compatibility issue with existing ammo stores. This was based on several departments getting surplus M-16 A1's with 1 in 12 barrels.
The other commercial rounds tested performed well, sometimes exceeding the mil-spec ammo. However, all of them had .223 cases, and the issue of reliability during full auto fire kept coming up. Only one commercial round, the TRU utilized a mil-spec case, but it did not have a history to compare with the other rounds.
For your Department, determine what your requirements are for the rifles, how they will be deployed and how they are to be used. From this develop the specifications for your ammo needs, what ammo your rifles can handle, and go from there. Good luck in your selection. Let us know what you guys opted for.