EveningSky said:
Voice and guitar (electric, electric acoustic, acoustic). I play with a percussive style; I frequently mic an electric solid body as well as the amp.
I am constantly looking for new sound. To quote: "microphones are to a musician like a paint brush to an artist."
I have read that tube mics have a unique and very appealing tone for both string instruments and voice.
I have never tried one out myself.
Here’s what I suggest you do...
Go here,
http://www.3daudioinc.com/mics.html and order the 3D Mic CD. Next, go here,
http://www.thelisteningsessions.com/home.htm and download all 5 sessions, plus order the Small Condenser Mic CD when it becomes available. Load all these files into your computer so that you can instantly switch between them for "back-to-back" listening. Study them well over a period of weeks. You'll be surprised at what you like and don't like. Also, take into account the preamps used - a Shure SM57, for example, will sound completely different running through a Great River than it will through an Audio Buddy.
Next, go to the mp3 mixing clinic,
http://www.homerecording.com/bbs/forumdisplay.php?s=&forumid=15 and find music styles similar to your own and find what mics and pres are being used to record them. Decide what you like and don’t like and why.
Finally, beg, borrow, rent, or buy using trial periods, any mic you can get your hands on and try it in every conceivable position. Then, you’re only going to begin to get a clue, but hey, it’s a start. By doing this you’re going to end up with a much better idea of what you need than anyone could ever tell you. (And you thought this was going to be an easy question to answer!

)
Otherwise, you may as well just close your eyes and pick one.
Seriously, this is the best advice I can offer you and is the same advice I use myself.