What music do you use to assess your system?

I like to listen to everything, all genres regardless of recording quality.

So I assess by randomly queuing up tracks to get a random sample of how things sounds overall.

Every recording is recorded differently, so I listen to make sure I can hear what is going on in each clearly, for better or for worse, and take note of the variations and unique aspects of each recording

Then I just listen to whatever I want to. If I hear a problem anywhere, I take note and address it, if needed.

Another benefit of using a random sample is that one is better able to determine when a particular sonic deficiency is common across multiple recordings (most likely a system problem) or not. If not, then sonic deficiencies can be attributed properly to the recording rather than the playback system

In the end well recorded large scale classical works always set the highest bar in regards to what it takes to reproduce them best.

For me in addition to that, to cover all the bases safely, I always want to test with various forms of music that includes well recorded electronic music elements just to make sure things are up too the task of delivering the goods at higher volume with this stuff as well without any noticeable rounding, breakup, distortion, limited dynamics, etc.

If those two things can be done really well chances are you are in good shape for most anything else less challenging that comes down the pipe.

Well recorded sound effects are actually very good for assessing systems because most people know what they really sound like.

Strauss waltzes on Telarc is well recorded with music AND sound effects.