Those topics are really fun :)
my five top are:

richie blackmore- the guy that could play anything in any style, and i think was one of the first sherders, all together with great feel

brian may - i dont think he is underated... everyone i know likes queen... anyway yes he is the king of the harmony

angus young - most energetic man to play guitar ever

jimmy page - great composer, great player, nothing else to add

andy summers, pete townshend , steve morse, steve vai..
i think this is it :)