Depends on how you say it and in which context.

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".

Depends on the tone.

I'm British

Therefore it ranges from "utter fucking shite but I'll say it a different way" to "moderately utter bollocks but bearable" right up to "yeah it's alright"

Worse.

See also: "Pretty close"

I'd say it means goodish

Worse.

Good

Pretty good

Really/Very good

Extremely good

Great

Pretty great

Really/very great

Extremely great

Awesome

...

Not necessarily worse, but more ambiguous than if I say something is good.

I learned about it the other day. Apparently native English speakers know than non native use it in a more positive way then they do

Good>pretty good

The word good is a stronger affirmative imo

Worse. Sometimes just a little worse than good, sometimes it's medium or negative but you're just trying to be nice. "How did you like the liver and onions I cooked for you?". "It was pretty good."

pretty good is less good than good

Same as good but it has limited impact

Depends on tone.