As for using different mics into the same board, it can certainly be done with no ill effects. But it might take your sound man a little longer to customize optimum settings for each. The SM 58 is the one mic that you can be confident every sound man is familiar with; if you're going through the house sound system and using the house sound guy, familiarity can be an asset.

I am currently using the Sennheiser 835 (one step up from the 825 that Jed mentioned). I like the sound, but notice that the proximity effect "fuzziness" is pretty pronounced -- lean in too close to this mic, and things start to sound muddy. Since I often play in high-volume settings where you have to "eat the mic," this can be an issue. Good mic, overall, though.

My advice -- if you're not confiden that there's something out there that YOU prefer, go for the SM 58, because it's a known quantity. In my experience you have to spend some time with gear before you can really evaluate its strengths and weaknesses; renting one for a night might not really tell you what you need to know. Also, as someone else mentioned, rental gear is often pretty beat up; it won't necessarily give you a good basis for evaluation. Good luck.