Federer at every age was more talented than Nalbandian. When they were younger they split their two most important matches, but Federer won 2 big tourmanents, but Bandy just 1. As they got older Federer continued to be the bigger talent. He could beat better players than Nalbandian.
Nalbandian whilst being a fantastic ball striker is vastly overrated as a player. He was never as good as Roddick, Hewitt or Safin. Coria was better on clay and Davydenko was his equal.
Federer, Safin and Agassi are the three most talented players for me. Stich and Sampras make up the top 5. In my time the last 22 years.