You only have to look at the rankings and what people have won to decide the winner and almost the order.
Nadal. 2 slams, 2 slam SF's and 3 masters
Federer. 1 slam, 2 slam finals, 1 SF and 0 masters.
Djokovic. 1 slam, 2 SF's and 2 masters.
Murray. 0 slams, 1 slam final, 0 slam semi's and 2 masters.
There's still a masters and the TMC to go.
The only thing you can ask is so far, is 2 losing slam finals better than winning 2 masters? I am not in a position to judge but one has 2 trophies at home and the other has 2 plates
I don't necessarily disagree with your conclusion, but you also have to look at who they played, and in that sense neither is particularly strong.
Both of Federer's losing slam finals came without playing a top 20 player, and the semi came without facing a top 10 player.
Nole actually won the Rome Masters with one bye, two retirements, and three victories, with none of those players being in the top 20.
I know you can only beat who's put in front of you and all that, but any half decent player would fancy their chances of picking up silverware with that level of opposition.
In fact, prior to the US Open and ignoring retirements, Federer had a 1-7 win-loss ratio against top 10 opposition this year. He's still only 5-8. Djokovic is better but still not great at 7-8. Andy's a comparatively healthy 9-6.
Not saying you're wrong, but it's something else to consider...
(As an aside, Ferrer still hasn't beaten a top 10 player in a ranking event in 2008 but is ranked 5 in the world, which I find a pretty amazing stat)