Prime is a very loose term. Players have prime years, they have peak years, they have prime years much better than others, they even have peak years better than others, matchups change, momentum changes. It is stupid to think you can create a definite ranking with all in their primes, as it would be the same each year in that scenario. However one thing for sure is Nadal would totally dominate clay with all these players in their primes, and that would ensure him no worse than a top 3 ranking. The points he would collect on clay combined with regularly strong (quarters or better of almost all events) on other surfaces, would make it impossible for more than 2 at most of the others to outrank him, especialy as there are too many tough hard courters for anyone to dominate there, and Sampras and Federer would not be able to dominate grass with the other there and with Agassi, Nadal (both benefiting from todays slow grass), Roddick, and Hewitt all challenging from behind.
, My eyes are still amazed at his old matches!
