I think for the moment Minato, but with better control of his BM he will win. Minato has much more experience in speed and is smarter. Naruto can't stay more than 5minutes in BM(only moment where his speed is compared to Minato). It's why i see Minato winning ftm but it will change later on.
Tbh i think it's Kakashi the one who will say if Minato is already surpassed or not since he is the one who compared them the first and he is the one who met both of them