It is tough with the different eras. I would have Havlicek, Pierce, and Tatum all about the same. You could make a case for any combination of 2 of these 3 for the SG/SF positions.
As to PF, same could be said about Garnett and McHale. Garnett was more important to the title that he won but McHale has a much longer tenure with the team and more titles.
For PG and C, there is not much question. Cousy was an MVP while in a Celtic's uniform. And Russell is Russell.