Nalbandian was the one player who, shotmaking vs. shotmaking, could beat Federer even when he was playing well.
Nadal owns Federer, but he does it by forcing Federer to play badly.
With Djokovic, it's usually also a matter of Djokovic forcing Federror to appear.
Same with Murray.
So it's close in terms of pure talent. Federer's always been much better mentally, physically, and he has a better go-to play with the serve-forehand than Nalbandian.