Not including Murray because I dont consider him important enough in the big scheme of things.
Federer - Nadal
I am actually being lenient to Fed here because...well, I am a fan what can I say. Actually, at this stage Nadal is likely to beat him everywhere including USopen too
Nadal - Djokovic
Rafa remains favourite at RG until proven otherwise and I am convinced he remains better on grass too, Nole played his best Grass court match in the Wimbledon final and Nadal a ho-hum GS final by his standards. On HCs however, its no cigar for Raf anymore methinks, though he will keep running Novak close with his trademark fighting spirit.
Federer - Djokovic
I know Novak has straight-setted Roger the last two AO semis, but the scoreline is really misleading there. Roger was leading by a break in 4 of those 6 sets IIRC. I also think had it been Roger-Nole in AO final this year and Nadal hadnt gatecrashed, Roger would have put stiff-Nole out of it. Just a personal feeling of course. On clay however, at this stage of their careers, Novak is favourite IMO, Roger RG histrionics from '11 notwithstanding. On grass, Fed remains the big favourite though and USO is really a toss-up. It shouldnt be if we consider how Roger should have beaten him the last two years also and been 5-0 but it is what it is.
As a Fed fan, I am actually happy he still has some chances against guys 5, 6 years younger than him. Its impressive especially if you look at the rest of his generation and where they all are.