Don't know why it's even a question if we're only talking about 2012. If we look at the past 12 months, Djokovic has a case because of the USO.
If we look at the last twelve months it's not even close.
But 2012 YTD, Federer is having the better year so far. Of course it can still change but right now, Federer edges it out.
I admit a case could be made for Fed if you value the small tournaments highly.