Cousy
Russell
Havlicek
Bird
Cousy and Russell were the center piece of the teams that won 8 straight. (Granted that Cousy retired in '63).
Havlicek was on tail end of the initial dynasty, and the best player/captain of the team that won 2 more, in '74 and '76.
Bird was the best player on the team that won 3 more; arguably the best player in the league during his prime.
I love Pierce, but he won a single championship, and, unlike the other 3, did not play his entire career in Boston.
No other player is in the discussion. McHale and Parish were really good, but that era we only won 3 championships, and Bird was clearly the best player and leader of those teams.