Well..my list is subjective but it is based on more than just the players physical style of game. I look at the player's current accomplishments, potential future accomplishments, style of game and intangibles (affect on other players for example). Hence, I stand by:
Federer = Sampras (Dominant, fluid players. Often have the edge in matches simply on reputation and presence on court. It's good for a few points here and there are against the majority of players. The intimidation factor. Also, talked about potentially be the greatest of all time which Becker is not even thought of.)
Safin = Ivanisevic ( Both highly talented players capable of beating the best when they're on but both psychologically "unstable". Big servers with the potential to do some real damage if they bring a complete person to the court. Safin, currently, has one more major than Ivanisevic.)
Hewitt = Chang (Both rely on strong groudstrokes and footwork to do the damage. Hewitt's slightly taller, more proficient at net and with one more singles major than Chang. Hewitt's also captured the no. 1 rank where Chang has only ascended as high as no. 2.)
Nadal = Muster (Both claycourt dominators that rely on the topspin to do the damage. Both highly feared/respected on that surface. Both lefties with RG's top prize in his position. Nadal has two to Muster's one. The only thing Nadal has yet to accomplish is the no. 1 rank.)
Nalbandian = Agassi (This was a tough given everything that Agassi's accomplished, but this comparison is based mainloy on potential. Nalbandian is one of the cleanest striker's of the ball since Agassi. Watching him play makes me wonder why he hasn't had a breakthrough in a major yet, but then Nalbandandian seems to have a bit of complacency in that he rarely feels the need to move his game up a level or is he capable of moving it up? Also, ala early Agassi, you can see the potential in the way he plays but I question his commitment to taking the step and claiming a match instead of waiting for it to unfold. His fitness is suspect as well as he's shown he can last in a five set match, but if he improved his physical assets maybe he wouldn't have to go five to pull out the win.)
Like I said. Just my thoughts. It's subjective. No "fixing" necessary.