Vulkan or DX12, which one runs better?

there isn't one answer, it changes per game and per card. just run both for the same stretch of the game with an overlay that shows 1% lows, not only average fps. stutter is where they usually differ. rough pattern i've seen: vulkan often does better on amd cards and when an older cpu is the bottleneck, dx12 is sometimes smoother just because it's the version the devs tested most. and ignore the first few minutes after switching, both stutter while shaders compile.