I think it is almost impossible to compare. Different eras, and different defenders in front. My personal impression would be a three way tie between Clem, Grobbelaar and Pepe. I think Clem read the game the best and was just about the best for positioning. Grobbelaar was the most athletic/gymnastic and could therefore 'recover' the best, and Reina has the best reactions I've ever seen, along with the penalties thing obviously. If stats say it's Pepe>Clem>Grob, then I don't think I'd argue too much. Never saw Lawrence et-al, and James, Dudek etc. are a league or so below.