The answer of this thread is clearly Davydenko. There is no comparison. They are both talented baseliners but Davydenko's achievements are so much better. Nalby barely owns any titles whatsoever.
From ATPWorldTour.com: "The 28-year-old Davydenko maintained his stellar record in ATP World Tour finals, improving to a 20-5 mark. The Russian is the 38th player in the Open Era (since 1968), and the fifth active player, to win at least 20 ATP World Tour titles.
That is some serious stuff. Safin can't claim that, and he has 2 Slams. Ferrero can't claim that either. And Rafter? And many other Slam champs.