Greatest and best are two different things. However both will be subject to opinion.
Greatest would be players who have been the most influential whilst we and/or they were successful. This would be players like Banks, Chandler, Schmeichel, Izzet, Elliott, Vardy and now Tielemans.
Best could be that but would essentially have individual brilliance. Players like Banks, Kante, Weller, Wortho, Mahrez, and Huth are a few that I'd throw out there.
It can be a fine line but that's how I see it.