I work for the company that builds most of GM's Reman and New crate engines (as well as current production service engines, Duramax, Mercury Marine, etc.). I am the Warranty and Quality Manager there. We have to follow the same IATF / ISO / Quality Management Systems that are required of any other automotive Tier 1 supplier. We have to use the same parts suppliers as GM, follow GM approved processes and procedures, and all of our engines are tested and approved by GM. In fact, a lot of our tooling comes out of the GM engine factory. As they wind down production engines and transition them into service only quantities, they will send us the tooling.
All that to say, buy a crate motor from an OEM if at all possible. The OEM's require their vendors to meet much more stringent quality requirements than your typical reman / mass builder operation. Obviously if OE's no longer support older platforms like the FE, you may have to look elsewhere, but if you are looking for anything built within the past 20 to 30 years, OE is the way to go.