Re: Which is/was the toughest task in tennis from 2005?
Nadal has the edge here in terms of invincibility and based on the date window having never lost in 5 finals. Federer with 4 final wins and only 1 defeat is not far behind. Djokovic needs to reach a few more finals at the AO to make a 5 final minimal comparison and win at least 2 of them.
The current greatness league of active players in order of achievements to date (a factual comparison rather than fan biased assessment):
Federer 19 GS, 6 Year End Masters, 26 Master Series.
Nadal 15 GS, 30 Master Series, 1 Olympic Gold.
Djokovic 12 GS, 5 Year End Masters, 30 Master Series.