Hesco, as a brand, is a standard in the industry. I have been pleased with RMA Armament on price.

If you are looking for rifle threat plates, I would look at something in the "III+" or special threat category. There are some decent plates out there that are rated for M855, which is probably one of the toughest common rounds to defeat. My hard armor for work, which is individually purchased, was selected for its M855 rating.

There are also some "IIIA+" varieties that have some rating for M193 ball.

Price, protection, and dimensions (thickness and weight) are the variables and unless you're spending a lot of money, you're probably going to be settling for two out of three.