it's not 50-50 Djokovic is better on hard at this point
Well, Djokovic is way better at the AO, which is slow hard court. Should they meet in Australia djokovic will be the heavy favourite.
At the USO I am not so sure though. It will obviously depend on the level fed is able to keep this year, but they met 5 times there, Fed won 3 and was very close in the other 2 matches having 2 consecutive match points both times, even in 2011 when djokovic seemed unbeatable.