In the USA, it seems that the fuel of choice for the OS 91 is Wildcat Jet A (5%). I have been using this with my .91 in a Dynamax with excellent results.
As for the 46 VXDF, 95% of the folks I know who are running this engine (including myself) are using Wildcat Jet A (10%).

If you do a search on this subject, you will find that there is no correct answer to your question(s). There are many choices of fuel and it all boils down to what is available in your area, and your personal preference.

Peter