I am probably going to sound like the others posting here XD
I found that I grew subscribers very quickly on Webtoons, espeically when I posted one page a day Mon-Fri, vs. 5 pages on a Wednesday (more pages posting during the week got me readers quicker than posting more pages one day a week, if that makes sense).
However, it's very hard for me gauge how much anyone is enjoying the story, or who is sticking around.
Also, since my pages are formatted more traditionally than in a scroll format, I don't like how my double page splash pages have to be 800px (I print comics, so I don't have the scroll set up which I think is better for readers on Webtoons).
But, having said that, there's pros and cons to both sites. All in all, I personally prefer Tapas because I love talking to people and I get more comments here than there.
And as mentioned previously, Webtoons doesn't alert you to comments, which I think is very poor planning on their part. Maybe there's a reason, but...I dunno man, I don't like not being able to engage easily with readers, should they choose to comment.
So my overall thoughts from my personal experience:
I think it's good to post to both to reach a wider audience, even if there's less personal engagement on Webtoons.
I like how quickly my readership has grown on Webtoons. And there's people I've met in person who only read on Webtoons, so it's good to have a mirror there.
I prefer Tapas on a personal level, due to the networking and community here. I like the people I talk to and chat with on my comic, and it's why I tend to not care how fast my subscriber number grows, because I'm still having meaningful (to me) interactions with readers. I feel a deeper connection to readers and other independent writers/artists here, than on Webtoons, and I think that's a failing of Webtoons as a platform, although it is clearly their goal to mainly provide comics to read, and not really foster a community. That seems to be working for them, so while it's a negative for me, hey, they have their own goals in mind.
If for some reason I was forced to chose between Tapas and Webtoons: because of my personal goals of being part of a community over numbers...I think I'd pick Tapas. But that's just because my goals are different than someone with greater ambition. I like Webtoons, and I like many of the comics over there, so that comment should not be viewed as a slight towards anyone who prefers Webtoons :3 But, still, if push came to shove, I'd be sticking with Tapas unless this platform really does something unforgivable XD
(I am still griping about the format change XD I guess I've gotten used to it though. ComicFury is where my personal layout really shines, as well as my main website.)