It depends on what I am doing and the type of exercise. For example if I'm on a treadmill or spinning I would look to put on a mix with uptempo tracks, remixes and the like. I love a good drum and bass track to power through.
However, when I'm doing weights I usually never finish a song so I skip between high and down tempo tracks to coincide with my workout and rest times.
Lately I've taken to listening to old school garage tracks from the 00's, so I'm never really consistent with my music selection!