User blog comment:Spike144/Risk of playing on unofficial servers/@comment-4795804-20130805092221

To answer both questions below:

The purpose of this blog post is to inform you that you can lose you saved data whenever you play on ANY server with an older version than the official http://ninjakiwi.com.

I'm afraid that nobody can give you either the list of "good servers" or the list of "bad servers", because nobody can guarantee that some particular server will be always on the the same version as the official one.