Let me start by saying that I personally felt this question was in a grey area of being on/off topic, so I didn't vote to close.
However, as I pointed out in my comment, you are using invalid MAC addresses on your interfaces. So the correct way to get unique IPv6 addresses is to fix your configuration.
That configuration really has nothing to do with ...
So, is it possible to make question like this to be "objective answer"-safe, and how should it look like?
To make it "objective-answer" safe, you'd have to stop requiring so much speculation about what you need. Furthermore, by asking for a one-size-fits-all solution, you're venturing into the classic "best practice" bad assumptions.