Fed easily. Nalbandian was a very fine ballstriker but he didn't have the power and athleticism of federer.
his feel for the ball and technique are certainly up there with anyone but talent is not just about how great your droppers and angle shots are.
athleticism, mental strength, willpower and hitting power are equally as important and fed was easily better than nalby in any of those.
It's no coinicidence that nalby didn't win more in his career.