Sakura with Cow´s Magic.
I just loled when I heard that
Round 1.- BASE forms.
Madoka (just realized madoka could defeat Walpurgisnaught at least in all timelines, though she did died in pretty much all of them, but her stronger forms one shot Walpurgisnaught)
Round 2.- 5-B forms
Probably Madoka, due to what Kyuubei said, not sure completely though.
Round 3.-2-A Forms (Speed equialized)
Not a match, Madoka is High 2-A, she is possibly 2-A.
Round4.- 2-A Forms
Not a match, Madoka is High 2-A, she is possibly 2-A once again lol.