For live work it's sensible to go for a bullet-proof dynamic. They are not the be-all and end-all of sound quality but they tend to stay working. Of those that stay working the Shures are maybe the ones that stay working the longest under the most provocation, but I'm very fond of AKGs too and still cherish an old D190E.

But you should not use the same mic for the 2 instruments, the EQ will need to differ, so you need 2 mics - although I'd suggest that the sensible choice if you want to play loud is to plug your guitar in rather than use a mic for it.