Different strokes for different folks. You would have to go with Martin, but they played in different positions and comparisons across positions and different times are virtually impossible. For every for there is an against that can be raised in the dicussion.
It really depends on how you define our greatest modern Tiger. For me, Richo for Richmond is like what Jack Dyer was for so many years. Legendary. And the thing with legends is that that is exactly what they are, a popular belief that isn't always authenticated. That is, the evidence doesn't always support the legend.
Richo was a great player in what were often diabolically poor teams, and it is hard to know what he might have achieved with better support around him. I do believe he never reached his potential with us, because he was always played as a key forward until very late in his career. It was like Richmond's first and foremost priority was finding another Royce Hart, and Richo was going to be it come hell or high water.
I don't think Dusty will reach those Richo/Dyer legendary levels at Richmond in the same way that so many of our other champions haven't, but I think we have already seen enough authentification through the honours he has won to know that he is a very special player. I think in time, on his current trajectory, Martin's name will be mentioned in any discussion of the best Tigers player ever. Richo probably wouldn't be in my top 10, much as I love him.
FWIW, my grandfather, a Tigers man for virtually his whole life (he was born in Richmond and attended his first game in the late 1920's), always told me that as good as Bartlett, Hart, Dyer etc. were, the best Tigers player he ever saw was Roy Wright by a fair margin. In his opinion, he has only seen one other player with the ability to so comprehensively dominate a game as Roy Wright could, and that player was Laurie Nash of South Melbourne. He considered Nash to be the greatest footballer of all time.