I don't see anyone with better results the last couple of years. When he's fit, I don't see anyone beating him.
Nadal on grass last 2 years:
2012 - Halle qtr final defeat to Kohlschreiber, Wimbledon 2nd defeat to Rosol.
2011 - Queens qtr final defeat to Tsonga, Wimbledon final defeat to Djokovic.
Federer on grass last 2 years:
2012 - Halle runner up to Haas, Wimbledon victory, Olympic final runner up Murray.
2011 - Wimbledon qtr final defeat to Tsonga.
Hard to support the assertion that Nadal is the best grass court player in last 2 years.