Who is your favorite heavy metal/alternative singer?

Personally mines serj tankian

Howard Jones and Benjamin Burnley (<----assuming that's what you mean by "Alt"😉 are definitely among the top. I'd have to think on the rest.

As far as Alternative Rock goes Elizabeth Fraser of the Cocteau Twins is number one for me.

Metal? It really depends on my mood, but off of the top of my head, and at this very moment, Sammy Hagar or Chris Cornell.