The SM57 and the SM58 are essentially the same thing, except for the 58 foam screen that makes it more suitable for miking singers, while the 57 is more suitable for instruments. They both are rock solid pieces of gear that won't disappoint, and when more sensitivity is needed, an external preamp such as a Triton Audio, Klark Teknik or a similar one will quietly provide more gain without the need for a more expensive mic. If you want to purchase one of the above mics, beware of the numerous fakes around, and buy only from reputable vendors.