Mai Linh is quickier. Both are tough to hurt. How ever she has neither the hitting power or grappling skills of Riggs.
And as quick as she was McClane who is far less skilled in grappling then Riggs is was able to close the distance and over power her. So Riggs should be able to do the same.
It should be noted however that if Mai had pressed her original attack and not left McClane alone to go back to taking over the world. She may well have finished him long before he gave her a rectal exam with an SUV.
So if she goes all out against Riggs she is going to make him work for it. In the end though I'd side with Riggs.