I have over 1400 subs on Tapas and 65 on Webtoon. 
It's good to be on both platforms, and I'd definitely recommend cross-posting if possible. Even if one platform vastly out-performs the other, you can still use one to advertise the "main mirror".
There are certainly some concrete things in favour of the Tapas mirror like:
- My comic isn't proper long scroll, more like two normal comic pages stacked and spread out a bit (four on webtoon). Webtoon seems to have a big preference for "true" long scroll while Tapas is kind of less bothered.
- I started on Tapas first and reluctantly added Webtoon when friends urged me to cross-post. I did that because I was fairly certain my comic was going to appeal to the Tapas audience more from the get-go just based on the fact that IRL friends of mine making comics for a similar audience (like Alien Heart and Buuza!) were doing well.
- My links on external sites and social media pretty much always go to the Tapas version because I just prefer the site and already have more readers here.
- I take part a lot in the Tapas community and events. I think there's a chance that was how I got my first feature- by being nominated for a community pick and catching the eye of the staff.
So it's entirely possible my following is bigger here because I put more effort in here. I could speculate other reasons to do with style, audience and stuff, but they'd be just guesses.
