I've worked with both 6.8 and 6.9 a fair amount. 6.8 is a fairly stable version, whereas I would not consider 6.9 a stable or even valid version.
6.8 has a few issues, which I believe are correctly documented in the 6.8 Known Issues list, and for the most part there are workarounds for those issues. I found 6.8 overall to be a significant improvement over all previous versions. I'm mostly referring to the quality of life type of enhancements. And of course that's when they added Edge Chromium support. I also found Chrome automation to be more reliable in 6.8 than it was in 6.7 and below.
It's just my opinion, but I would not recommend anyone upgrade to 6.9 without first doing significant testing in it from an evaluation/playground environment first. The thing to pay attention to is Chrome/Firefox/Edge browser automation in regards to the speed at which it runs. There's also an issue with 'Evaluate Expression' when it needs to work with a collection; that is, it just doesn't work at all; and this might sound like a small problem, but it's actually pretty significant problem for developers.
I personally think 6.9 should get deprecated (and the installer removed from the Portal) once a 6.9.1 version comes out or maybe 6.10.
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Dave Morris
Cano Ai
Atlanta, GA
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Dave Morris, 3Ci at Southern Company