Based on what we've seen from Shakur so far? Nazarov. He was a very underrated technician, with a lot more firepower than Shakur. If Shakur has an extra level that he can bring out versus Tank, then I might change my mind on this matchup in the future.
Shakur hasn’t shown anything that would have bothered Orzubek. Unless he manages to beat Tank in convincing manner I don’t think Shakur has the style to beat a killer like Nazarov.