Which one was/is more impressive?
Both of them are 1-4 in finals, but
Federer proved he can beat anyone at RG except Nadal. His biggest match win was against peak Djokovic in 2011.
Djokovic scored wins over Federer/Nadal/del Potro and it is arguable he would have beaten Murray if they played a few more matches there, but he usually doesn't deliver/chokes in the final.
Both of them are 1-4 in finals, but
Federer proved he can beat anyone at RG except Nadal. His biggest match win was against peak Djokovic in 2011.
Djokovic scored wins over Federer/Nadal/del Potro and it is arguable he would have beaten Murray if they played a few more matches there, but he usually doesn't deliver/chokes in the final.