Both AMD and Intel seem highly supportive of OSS.

Intel's iGPUs had the best Linux drivers for the longest time, while AMD just managed to mainline their GPU drivers into the 4.15 kernel.

I think AMD is "worse" at it but for understandable reasons. They're a smaller company, so it takes a bit longer for AMD to release low-level manuals. (Ex: still waiting on those Zen architecture instruction timings AMD!!). Even then, AMD releases "draft" manuals which allow the OSS world to move. So the important stuff is still out there, even as AMD is a bit slow on the documentation front.

Basically, Intel is a bigger company and handles the details a bit better than AMD. But both are highly supportive of OSS in great degrees.