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.
NadalAgassi: I think Serena's final slam tally will be something from 18-27. My best guess is 24 or 25 though; Nole(2010) will never win Wimbledon