and that's a very valid concern. some mics just simply don't work on some voices. the only mic i have that has never been bad on anyone's voice (sometimes it's fantastic, at worst it's just okay) is the shure ksm32, but that's $500.
if it all possible, you want to line up a number of mics, preferably using the same mic pre as you've got, and see what you think. record each and play around w/ EQ to see if you can dial in the right sound (sometimes the right sound isn't so obvious at first).
even better -- sing to a song you have that's somewhat pre-mixed and see how easy it is to get your vocal to sit right with each mic. once you've done that, you've found your mic.