I have always used the Shure SM57 for both vocals and miking my acoustic guitar. The SM58 "Ball" may be preferable for vocals (the response curve is slightly flatter) but they are both built like a tank, virtually indestructible. My son recently bought an AKG ribbon mic that he likes a lot but it was somewhat more pricey ($200-ish as opposed to about 90 for the Shures) and far more delicate.