I'll start first: Product Hunt, more specifically their forums/discussions. IndieHackers works better for me (although PH traffic is 10x larger). And yet, I got way more feedback about ZeroToUsers.com from IH vs. PH, and the quality of people that came from IH was much much better.
What about you?
Google Ads! Our marketing so far has been limited to posting on Reddit and IndieHackers, which brings in quite a bit of traffic and sales. So we thought we were ready to scale with Google Ads.
What we had forgotten is that we built logology around startups needs, which are pretty different than your common SMB who searches for "logo generator" on Google. Conversion is terrible from Google Ads at this point, and we're back on finding marketing channels that suit us better.