I think that Moorer gets to Mildenberger quite easily and quite ferociously- Joe Louis made the easily seen observation that Mildenberger would drop his left often, and with how slow and plodding the German could be, I don't see him making it very far with Double M. Quite the fighter though, that Mildenberger. Drew with Folley, had Machen quit, and gave Ali a hard fought bout- Though I'm sure most good southpaws would've given The Greatest some trouble.
Moorer all day. Moorer had a pretty deep amateur background that saw him fight a lot of fellow southpaws which is something that Mildenberger didn't see in his era. Prime Moorer was a really good combination puncher with an excellent right jab and superior power to Mildenberger.
IMHO the difference is in class in favor of Moorer. LHW Moorer Vs. Mildenberger - we could discuss that.