I hope this is the last 2.1.x release and that the next release will be Tracks 2.2 containing a lot of improvements. You are welcome to help test Tracks 2.2. In the mean time if you prefer the stable release, 2.1.4 is the best choice.
Please note that Tracks 2.1.x does not support ruby 1.9 and it depends on ruby 1.8.7. Tracks 2.2 will support both ruby 1.8.7 and ruby 1.9. After 2.2 support for ruby 1.8.7 will be dropped.