I am inclined to go for Sands, nobody wanted to fight him after his wins against Bobo Olsen (twice) and a 1st round KO of Dick Turpin. I have read about Sands and Robinson knew of him but thought he was to dangerous, sadly he died before a fight could be made. Homesickness was a problem for Sands.
I disagree with VD about Kostya considered Russian, his professional career started in Australia and he is an Australian citizen, without his Australian team i doubt if he would have achieved what he did.
Fenech was good but IMO could have done more, losing to Grove was a blackmark. The Holiday loss was embarrassing.
Both Famechon and Rose were good fighters but not great, Rose beat Harada and Castillo before losing to Olivares and Famechon beat Legra and Harada twice before losing to Saldivar ( Shocking decision) so there is some merit in their careers for sure. Mundine, Green and Briggs have a fair way to go yet.