I use a metal curry all the time, but the kind I use isn't available in the US, you have to get them in Europe. I have a rubber curry too, but my guys just love the metal one because it really gets all their itchy spots. It makes their hair very smooth and shiny.
My favorite tool isnt a brush at all though, its a damp towel. I wipe my gueldings down with a damp towel each time I groom them to get ALL the grime out of their coats.