The thing about sloping ones is that it simply redirects the air towards the bottom of the tire, not towards outside of it (away from it).
I just put a simple flat splash guard, but much bigger than yours in the first pic, for sake of easyness.
But I would think that a Convex shape would be the best by far since it would direct air towards the sides (away from the tire). It just becomes a little more complicated to do so
