I wouldn't count Murray out on grass.. Federer might still be the best right now, but it has always been Murray's fave surface, not necessarily his best, but his favourite. If Murray wins Wimbledon this year, he could certainly win it again...
As far as dominance between the two, no, I just don't see it. Tomic and Dimitrov will eventually breakthrough meaning the slams won't be dominated.
Murray always said Clay was his favourite surface