very legit question this is.
I would personally rank him fourth behind marshall, ambrose and holding; and slightly ahead of garner. apart from the first position that rightfully belongs to macko the other four could easily swap their positions. and the thread starter would hopefully admit that my ranking is not based on stats alone.
i am sure my opinion is heavily colored by the fact that by the time i started watching cricket in the early 80s roberts was slowly making way to marshall to lead the pack with holding and garner hunting batsmen full swing. otherwise, in terms of quality, jeez, there is no way to split these guys. croft and walsh would have to stay one step below these five giants though.