I'm not going to attempt to rank the suggested players, there has been plenty of discussion about them while other players have cropped up occasionally in various posts.
What I will do is comment on some additional names and those mentioned only briefly.
There has been plenty of tributes regarding Sehwag, and rightly so. Other opening bats have also shown to be more than efficient against spin - Sunil Gavaskar for one. However, I'm going to highlight two visiting openers who showed they were good against spin. In 2001, after losing the opening Test, India won the BG Trophy 2-1 with some mention being made of the pitches prepared. Apart from Matthew Hayden, only Steve Waugh managed an average over 35 for the Australians. Hayden was outstanding. He scored 549 at an Bradmanesque average of 109.80. In 3 Tests he scored 2 centuries and 2 half tons.
Almost in the same league as Hayden is Alastair Cook. In the 2012/13 tour of India, against an attack that included Ashwin, he scored 3 centuries in the 4 Test series finishing with 562 runs at an average of 80.29 while Ashwin was reduced to his worst home Test series (14 wickets @ 50+) due mainly to Cook's batting.
Apart from Hayden, not many Australian's have come into consideration in this thread. Ian Chappell rated Doug Walters as Australia's finest player of spin while I would rank Damien Martyn above Michael Clarke who was mentioned earlier in this thread.
Others mentioned occasionally, but warranting greater credit, are Younis Khan, Zaheer Abbas, Javed Miandad and Alvin Kallicharran. The latter averaged 58.35 in India but only 38.72 elsewhere.
