Probably Windows, because on Linux you have the AMD mesa driver and perf and valgrind-callgrind and kcachegrind which are all pretty good. For OpenGL there are renderdoc and apitrace. Unfortunately, the rr reverse debugger does indeed not work with Ryzen because the performance counters are too fuzzy, as mentioned in another comment.

I have been working with performance tools on Linux for over 10 years and occasionally debugged graphics issues.

kcachegrind is okay, but VTune is a lot better.

Our game actually ships on Windows, macOS and Linux (as well as the two dominant mobile OSs), so I dabble in all of those platforms. The Linux OpenGL performance is indeed better than on Windows, but unfortunately it makes up only a super small fraction of our userbase.

I should note that the OpenGL stack on macOS isn't better than the Windows one either. Probably not surprising anybody, given the lackluster support that Apple has for it. We are seeing similar improvements with Metal as we do for Vulkan.

Yes, Mesa/Gallium is much faster than AMDGPU-PRO and Windows driver junk.

Windows OpenGL driver is so bad that running it through ANGLE with DX backend is faster.