Thank you for asking this question in the support community. Currently, we do not have a document that explains the differences in firmware versions. Until that document is published, either of the versions you listed above would be great to use. For a general overview, in the firmware version R10.x.z, "x" is the feature release number, and "z" is the maintenance release of that version. I recommend you review the release notes for the firmware revision to determine if you need any of the features or enhancements that were released in that firmware release.
Please, let me know if you have any additional questions. I will be happy to help in any way I can. Also, I will reply to this post with further information about the different firmware releases, when that document is published.
For future reference, here is the Upgrading Firmware in AOS guide.
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