There are plenty of great options: Giggs, Scholes, Baresi, Maldini, Facchetti, Puyol, etc.
For me though, the greatest is Francesco Totti. The others above played for clubs who won multiple trophies, and all won the champions league at least once. Aside from a smattering of Coppa Italias and one Scudetto, Totti didn’t win anything with Rome.
For me, it’s easier for a top player to stay at a top club, rather than be a top player like Totti and stay at a club that was rarely considered the best in Serie A. For my money, he is the greatest one-club man of all time.
Who would you choose?
Jonas Hector… Great player, Allegedly turned down Liverpool, Bayern and Barcelona to stay with his boyhood club Köln.
I’d wager its easier to be a one club man when playing for a great team* (although probably not an elite team) yet Despite being a regular for the German national team he stuck by the bundesliga/2.bundesliga yoyo team thay is Köln even through relegation eventually retiring there this year.