In terms of who I personally saw play live, I have to say that Gullit in his latter days at Chelsea was still a truly astonishing player. Whether you wish to call him a defender or whether you wish to call him a midfielder in a defensive role, I saw him effortlessly keep the cream of the premiership striking talent in his pocket before setting up attack after attack with a perfectly weighted pass.
I'm sure the Milanese back line were techincally better defenders and all that, but I never actually saw them play live.