I'd go with most of that list, but probably go with Robinson or Marciano over Moore in the 50s. I also would have picked Jack Johnson over Gans and also possibly over Langford too in 1900-1919.
Leonard may well have got my vote in the 80s, his wins over Hearns, Duran and Hagler enforce this but Larry Holmes and Mike Tyson deserve a shout too though.
Lastly I'd have probably shaded Gene Tunney over Leonard in the 20s.
As for the first decade of the 21st century, Floyd just gets my vote.....Roy Jones was clearly the man till 2004 though!