Bob, for the money, the SM-57 is unbeatable. I've used one for decades. It doubles as a tack-hammer, it's that rugged!

My understanding is that the SM-58 uses the same element but yields a better response curve for vocals.

Chet Atkins; Emmylou Harris; Mark Knophler; et al, who could easily afford any mic made, chose SM-57s for this concert. Convinced me.