Better vocals

Robert Plant from Led Zepplin
Freddie Mercury from Queen

I am struggling with this question just between these two.
I know there are more names like these guys like Steven Tyler
but just between these two guys whos better?

Anytime Plant's name comes up I always hear this song in my head. Sure its a little slow and methodic for most people but its just got this smooth steady guitar work that blends with his voice in such a way Ive never heard before.

Ohh and Freddie Mercury is better compared with the likes of Roger Daltrey. More along the lines of good bands/vocalist as opposed to great bands/vocalists like Tyler, morrison, Palmer ect...

Mercury was good and all just not on the same level as Palmer. Not even close.