3
Use 2.0.15 - Make sure you apply the form fix in my sig.
2.2.5 will be an update release for 2.2.4 - fixing a few issues, but other than that - it will probably be the last release on 2.2.x
Other than any maintainance releases - 2.0.15 will probably be the last major release of 2.0.x, and the next will be 2.3 (when finished). 2.2.x users will probably have to wait until 2.4 which is a while off, before they can update.