RMA or Apex for good stuff, excellent vendor support if needed, reasonable pricing, and product quality. RMA has a longer ship time than Apex. i generally provide Hesco and RMA plates to law enforcement. Hoplite is okay since they are rebranded LTC plates, but you will not get LTC support or warranty. both Hesco and RMA warranty the plate itself, although Hesco has no individual sales unless you are government agents or security corporation connected. i've heard good things about buying Hesco plates from TREX ARMS, but never did it myself or through my business.
if you're curious, the military gets plates through the vest supplier (Rothco, Eagle Ind, Crye, et c). 3M is the only company that sells SAPI and ESAPI plates as a little pack by itself, although i don't think they're available to individuals.