I agree with Gizo that Lendl is very underrated. He's not Federer, but he should be ranked #1 in the 2nd tier great. Connors, Agassi, Mac doesn't doesn't hold tennis records like Lendl, who also was more consistent...multiple years with a 90+ winning percentage.
Federer > Davydenko > Nadal > Federer
Nadalgaenger: "Djokovic is clearly better than Pete"