Describing a firmware release as the "best" would be meaningless. Each firmware release fixes bugs in previous releases, and/or adds some new settings or features. Sometimes, a new bug is introduced and missed during testing. All we can say is: the version link I posted is the latest I know of, as of today, and it could be supplanted by some other version at any time, and, it is working reliably so far.
Since Obihai doesn't consistently provide release notes, we have no way to know what changes. Since the firmware is rather mature, most changes happening these days are fixes to obscure bugs discovered by a service provider partner, or a setting added to support one or more service providers.
If you keep your firmware up-to-date, AND you keep copies of the previous firmware .fw files, then, even if a version update breaks something, you can typically go back to the last known-good .fw.