Strongest does not mean you can win
Anyway, this would be a tough one. There is no doubt about it that Negato is much stronger then Minato, and has a wider variety of Jutsu, Shinra, Chibaku, etc. but we have to acknowledge that Minato is a genius like no other, the smartest in the Narutoverse by far. What we do know about Minato is that he has frog summons, in which he could combine elemental attacks like Jiraiya taught Naruto, Rasengan, tons of sealing jutsu from the Uzamaki clan, and the Dangerous FTG.
That is the one thing that is so hard in determining this fight, is the lack of knowledge from Minato's full arsenal. We don't know about all the sealing jutsu, but we know there are powerful ones like Dead Demon Seal. I am completely at a loss on this one, but I don't think it will be a easy fight for neither of them, especially Minato, but since he is probably the smartest ninja in the whole series, I wouldn't count him completely out.