Since Kaveri AMD started building in the "Platform Security Processor". That's an ARM core that provides Trust Zone feature (ie. "make Hollywood trust your computer, despite you, the user"). Its code is signed as well.

About the same time they also stopped releasing source code for hardware initialization.

So along that axis they're not significantly better or worse than Intel nowadays. (I guess you can get by with a smaller firmware, and they allow redistribution, which are both nice, but not very relevant for freedom or security purposes)