I play solo piano with backing tracks four nights a week, and have examined every app geared toward this. For my money, OneTrack is the best of the crop by a considerable distance. The ability to create your own set lists independent of iTunes is a major factor.
There are many ways to work with the app, I create set lists based on style (bossa, rock, med jazz, up jazz, etc., plus lists for A-D, E-H, ec for fast alpha sort, as well as pre-selected full sets, and one everything list. This lets me choose how I will operate on a daiy, or set-by-set basis, whichever seems to be most appropriate for the crowd.
The app lets me switch quickly to whatever I need, and (the true test) my tips have increased since switching apps - I get to requests faster...)
The author has been VERY supportive, I highly recommend this app.
The_Soundsmith about OneTrack - Backing Tracks for Pros