I couldn't even begin to start ranking them by effectiveness tbh. It all feels so varied and kinda random xD
For my first comic I stuck to Facebook/Instagram/Twitter, with mirrored content across the 3.
From those, my audience on instagram grew the most, but I'm not sure how many of those people actually converted into comic readers. A big downside of that platform is the inability to include clickable links in the caption. It also had my best engagement though so that's something!
Twitter had my 2nd largest audience, but also the lowest post engagement so I'm similarly not sure how much mileage came from it. One nice thing is those accounts that auto-retweet certain tags which is useful for at least some additional reach (although how many people actually look at those accounts is another factor xD) I feel like I ultimately don't use Twitter often enough for it to be truly lucrative for me though.
Facebook was a mixed bag. The majority of my audience there is, understandable, folks who i know irl and who wound up liking my art page. My posts there get low engagement so I thought it wasn't very effective, but I found out after the fact that a lot of my friends/acquaintances actually were checking out my comic from promotions there, they just weren't liking the posts nor had Tapas accounts but I'd run into people at parties and stuff and they would come up to me and talk about how much they liked my comic and I would just be like "oh, you've read it? nice!", knowing that facebook is the only place they could have seen it.
Overall while I don't mind any of these platforms and will continue to use them in the future, I've kind of given up trying to really pursue "growth" on them. Twitter was perhaps the worst offender, but the type and frequency of content you have to make on standard social media like those is just... not my favorite to make and I can't get enthusiastic about writing several posts a week.
Two new platforms that I'm hoping to incorporate into my new series' promotion are Twitch and Youtube. I've been streaming on twitch for about 7 months now and have been having a great time there! It's so so much more fun for me to do live content like that and interact with people in real time rather than writing insta/twitter/fb posts lol. The visibility for artists on that platform is pretty poor, tbh, but I've still made some strong connections and have managed to get people hyped about my new comic before it even launches, just by working on it on stream for several months ahead of time.
Youtube I haven't technically started yet (I have a few old gaming videos on my channel, then a trailer for my first comic from 2 years ago, then a few speedpaints) but I'm gearing up to launch my first comic tips & tricks style video sometime in the next week or two. That's been fun to work on too, and I really see the potential in Youtube helping to get eyes on your work if you approach the content that you make in a smart and strategic way.
So I guess for this new comic, it will be the wave of "video advertising" for me. Can't say which platform among the 5 (fb/twitter/insta included) will do the best this time around, but I'm at least having a lot more fun streaming and making videos than static posts~