What songs do you listen to to test a system's midrange performance?

I have a pair of self designed open baffle DIY speakers (check out pics in my virtual system. Everything is the same except the power amp which is now an Audio Research DS-450). These speakers sound very good, I hear more now than I've ever heard from my music in the past. I've ordered a pair of the Caladan speakers from Clayton Shaw, but they probably won't arrive until next month. I plan to compare the 2 pairs of speakers. Since the midrange is where the heart of music lies, I'd like to know what songs you use to test the mid frequencies on your system (or when you incorporate any new equipment and/or tweaks).