Depends how you mean. Nadal makes federer look bad with the overall head to head but he hasn't really slaughtered federer that many times. a couple of times in Miami and the rg final in 2008, also iw recently but considering his age now and his physical issues i don't think its a terrible loss.
Fed has some total demolition jobs vs hewitt and Roderick but are those great of the game? Depends what you mean by great. he also has some heavy wins over Nadal and djokovic - the 4 matches where he bagelled them spring to mind.
Djokovic and Murray have points in their favour too. djokovic his whole 7 match run vs Nadal and Murray has that Olympics final and a couple other matches vs fed and Nadal.
Overall in terms of head to head Nadal is the best at making great look bad, in match play possibly federer who is nearly always competitive vs any players but can totally outplay rivals when he's on form even recently.
Special mention for nalbandian who made fed, Nadal and djokovic all look bad in Paris and Madrid 2007.