My idea is that they are all 30.0. The numbers after the - are numbers from the different packagers and will depend on what those packagers use as numbering system for their own purposes. The contents of those may thus differ according the whim of the packagers. Thus a “higher” number does not mean “newer” (except with the range of a particular repo).
In general I am conservative and like stability, I only use the “official” openSUSE repos that will provide me with the security and recommended updates. These are normaly retrofitted to the version shipped with an oenSUSE version. Firefox is different because Firefox does not provide security patches, but only newer versions that, when you then update to them because of security, surprise surprise, also contain new “features” which will hit you of course when you can not afford it.
When you say you want the “latest but stable” verion. that is contradictory wording imho ;).
It is always a trade off and you decide. I decided to use the Update repos only.