Vanax 75 has been discontinued so by default Rex 121 has to win.
However, the question remains, if Vanax 75 was in production, what would you want to do with the knife in these steels? Rex 121 is approaching ceramic type levels IMO for wear resistance but will not have the corrosion resistance as Vanax 75.
At the end, like all steels, pick the steel, heat treat and geometry to suite the task you want to perform. There is no be all end all in steels.