My two cents:
1) pick music that inspires you to teach. If you ReALLY hate your music, it will come out in your teaching
2) you can't make everyone happy. You are bound to encounter music complainers. Don't take it personally. By having a variety of styles in your mix, there is probably a little something for everyone
3) please don't sing to your music. I see some instructors singing away. ugh (need i say more).
4) delirium and crystal method are probably two bands that i use a lot in my spin classes.

Happy Spinning!

hannah