So far, the platform that worked the best for me is ComicAd. Seriously, I can't recommend the place enough. It's best if you have your own webcomic site (a ComicFury website can also do the job), as it will make possible for you to host ads and gain some money, which you can either invest into more advertising or you can withdraw once you reach $25. I've been on the platform since late March 2021, invested into it a grand total of $8.76 and... my view count on ComicFury literally exploded. Went from roughly 7k views/1200 visitors to 15k+ page views and over 3300 visitors since I started. And... I even earned $1,52, which, judging from what I could read on the forums, is about 10 times more than whatever money Tapas ads give you? XD my webcomic site is pretty small, I only have 23 subscribers on ComicFury, BUT I could definitely see a big improvement in my stats ever since I started to use the network, with at least 10-13 visitors checking out my comic on a normal day and an average of 45+ visitors and 200+ page views on update day.
The great thing about ComicAd is that you don't even have to pay for ads if you don't want to! Once you register an account, you can simply upload banners for your comic and the site will automatically show them on comic sites that have available ad space. Pretty sure that's how I got one of my most recent subscribers on Webtoon (put a free banner on there, the banner got a click, on that very same day I found out that I had a new subscriber... and no, it wasn't update day). So yup, definitely recommended <3
As for other platforms:
Instagram is where I get the most interaction. Not sure how many people actually read my comic from there, but they DO like posts where I mention comic updates and my stats on Tapas seem to increase a little when I post on there, so there must be at least someone who actually checks my comic.
TikTok is... fun and easy to work with (even though I never had a video going viral XD), but I doubt I got any readers from there. Comic pages are the videos with the lowest amount of likes on there... yet illustrations featuring my characters tend to be quite successful, which makes me think that users are mostly there for the pretty pictures rather than finding stuff to read XD
Pillowfort is where I spam all of my comic updates. Got a couple of readers from there, but again, the great majority of my followers seem to be in for the watercolors and random illustrations, rather than comics. Not comic related, but I did get to make a bunch of sales on Redbubble thanks to the platform, though! (AND got a job offer, too ^__^)
Haven't tried posting my comic on Deviantart, but I had a little bit of success promoting my watercolors and Redbubble prints.
Twitter: a wasteland where nobody cares about what you post. Stopped even trying.
Tumblr: a wasteland full of drama and pr0n bots. Still recovering from the emotional trauma after 10+ years spent in a community of backstabbing cyberbullies. Not touching the place with a ten foot pole
Artfol: very nice, but... I kinda tend to forget that it exists :'D I'm afraid I have too many platforms already.
Reddit: got some really nice feedback on there and even a few new readers on Webtoon... but also got a 1-star rating bomb. Not looking forward to have my comic downvoted again (especially since the rating would probably drop down to 4 stars if trolls decide to downvote it again), so I'm either posting panels with no links or not posting at all
Youtube: posted a few speedpaintings on there, but can't say that I put much time into it.