this one or selena gomez's version?

I absolutely think "A Cinderella Story" with Hilary Duff was the best Cinderella movie, espcially out of these two.
Selena Gomez's version - "Another Cinderella Story" also had several good scenes and I thought it was entertaining, but it also had several ridiculous scenes that I wish had been cut out.

And I don't really think that Selena's version can be called a "sequel" to Hilary's version. It is good that they called it "Another Cinderella Story" instead of "A Cinderella Story 2" - as the real title ("Another...") doesn't make it obvious that it is intended as a sequel.
The whole concept of Cinderella is a very old, universal story that has been told and retold numerous times, both in books and films. Movies with different actors, characters and unrelated plots (plots that don't fit with the first film) that still claim to be "sequels" to previous films is just ridiculous, and I think those movies could do better if they are promoted as "their own". A movie claiming to be a sequel will always be compared with the first film - and this is often not to its advantage).

Anyway, since there are many different interpretations of Cinderella, I think these two movies should be just be considered as differetn versions / adaptions / interpretations of the Cinderella fairytale. They have that in common, and the basic plot line of average girl being treated badly by her "evil" stepmother and stepsisters meeting the "prince" and after some struggles wins "the love of her life" and they "live happily ever after" - is the same for all Cinderella-related stories. Other than that, these movies are very different. The characters are completely different people, played by completely different actors, and the storyline and incidents are different. So the movies are not related other than the fact that they are based upon the same theme. Thus, "A Cinderella Story" and "Another Cinderella Story" are not prequel and sequel, but two seperate movies.