2
The quick explanation?
2.2.x is a brand new version with new features. It is still in a testing stage at the moment, as there where some problems with its earlier releases. The testing is going very well however.
2.0.13.2 is based on the current release (2.0.x) - but the security issues recently discovered mean that it is sensible to update this version, while people wait for the 2.2.x version to be released.
You can update 2.0.13.2 to 2.2.x when it is ready for release... but make sure modules you use have a compatible version first.