0.2.3 is nothing more than 0.2.1.1 with trivial fixes to make iTunes 5 work.
Nightlies past february or so already worked with iTunes 5. So really, 0.2.3 is really 0.2.1.1, and nightlies are “newer” — i.e. based on the sqlite backend rather than the gdbm backend, has transcoding support, has itunes xml support, etc.
So yeah, nightlies are “newer”, and also work with iTunes 5.