I think that Shrek is one that should be in the top 10. He has wins over Burns and Hart, although he was beaten by O Brien and a couple of others. I never actually realised just how good O Brien's record actually was. And he was considered the world champion for a while. He had wins with Choynski, Maher, Hart, Shrek, Ryan, Fitzsimmons, Kaufman, Flynn, Not to forget the ND with Johnson. I have always been put off by the big ko losses he suffered, and the reports of him turning and running against Burns, but maybe i was taking Komptons word as gospel too much. I thought it was he who mentioned many fixes and poor showings. HIs win loss record makes him definitely one of the best of the decade. And, it adds to Fitzsimmons ledger in the decade, which included Ruhlin, Sharkey and O brien (and of course the Dunkhorst victory which is often quoted on his ledger) and i think he deserves plenty of credit. The early 1900s Fitz, IMO (head to head) is in the same class as Johnson and Jeffries, maybe a little behind. The Fitz who knocked out Ruhlin and Sharkey could have very easily done the same to Johnson and Jeffries if they had met in close proximity to those matches.
O'Brien is one of the few high profile fighters to admit to several "Fix" fights but he was a fantastic boxer if a little chinny.