Third-party GUI rendering

Hello, I’m planning to add NanoVG support into my game for GUI.
GitHub - memononen/nanovg: Antialiased 2D vector drawing library on top of OpenGL for UI and visualizations. NanoVG is small antialiased vector graphics rendering library for OpenGL (there is DirectX port).

So I have a few questions:

  1. What would be the best way to render it on screen (the fastest way)?
  2. Which version of NanoVG would be better to use OpenGL or DirectX?