Depends on how you say it and in which context.
A shrug and a “pretty good” = acceptable, not worth complaining about.
A slow grin first or it being said loudly = better than good, great.
Although this depends on how emotive the speaker is.
My Bad-to-Good spectrum would be:
Bad
Pretty bad
Fairly bad
Fairly good
Pretty good
Good
“It’s not bad, but it’s still pretty bad” is a phrase I can see myself saying. Not sure about the other way round - doesn’t really work for me, but to each their own…
For me, it all depends on tone of voice, and what word is emphasized. “Pretty good!” generally means better than expected. “Pretty good” is like “Good, but…”
Neither, really. I use it to mean “more than expected”. Like, if my kids insist I watch a cartoon with them, and I enjoy it, i’d say it’s “pretty good”. Or if a coworker said something awful about a customer, I might say the comment was “pretty mean”.
it can mean “decent, better than I expected”
or
“good, but not exceptional or memorable”