As others have said, it depends a lot on the product. A lot of the people on PH are other people building stuff, if it makes sense to launch there, join some PH communities on LI. The more you're already engaged on PH, I think the better off you'll be.

I've found it's harder to read signals from ads for early stage releases. You need something to compare to... Then again, maybe a super narrow target with a very clear conversion might yield some useful engagement.

GL!