Our best artist friend has had different results. Here on Tapastic they have 2.6K subscribers and 170K views where as on LINE they have 900 subs and 13.7K views. So for them Tapastic is the better of the two. That being said, to the best of our knowledge, they did receive a total of four staff features, a Staff Pick and three Daily Snacks, which obviously had a huge effect on their viewership.
LINE does have a larger readership by far. Tapastic recorded 7.1M visits in January whereas LINE had 21M, so yes, there are 3x more readers at LINE over Tapastic.
Creators have the choice to publish wherever they want. In fact the Director of Content at Tapastic encourages posting in multiple locations. So rather than think of Webtoons OR Tapastic think, Webtoons AND Tapastic. Use them together to help your viewership grow. The only difficult choice to make is picking which one you want to send all your advertising/marketing/promotion traffic to because obviously having a huge following at one location is going to push you up the charts better and make you more visible than two smaller equal followings.
We agree that its very hard to get "discovered" here on Tapastic. "Fresh" isn't what it used to be. When we joined back in May 2016, Fresh lasted much longer and our first series was able to get some eyes on it. We ended up on "Trending" several times because of that which really helped us grow.
Since then, Tapastic has doubled in size in terms of total number of series and daily episode updates, but the readership has only increased by 22%. Since 2x as many series are competing for 1.2x more readers, it makes it very hard now for a new series to take off unless the creator is already established and can utilize their existing readership.
Today Fresh doesn't last very long and is no longer a dependable source of readers. It used to be we would get 10 or so subs out of Fresh, now we get 1 or 2. Trending is also much the same. It doesn't last very long (one of the developers said Trending updates every 2 minutes during the podcast) and a lot of readers are now choosing to completely bypass the homepage because its static (they're tired/bored of seeing the same series on "Popular" day after day). We used to get 40+ subs out of an hour on trending. Last time we were on Trending was probably the first week of January and we got 10.
We have two series on Tapastic and the difference in their readerships are night and day. The one that started in May 2016 is a much larger readership than the one started in December 2016. The one in May is in a small genre ("gaming") and so its much more visible to those who go through by genre, so it picks up a steady amount of subs even if its having all sorts of artist health issues that are forcing it to remain at a standstill. The December 2016 series updates like clockwork and is growing far less than the May 2016 series because its a "fantasy" which is a very large genre to get lost in, plus Fresh isn't what it used to be.
Our opinion is that certain series are going to do better at LINE and certain are going to do better at Tapastic. We don't know much about LINE so we aren't going to comment on it, but as far as Tapastic, if you think your series can get a staff feature, you are likely going to do much better at Tapastic. Series that are most likely to get a staff feature are short form, comedy, slice of life, gag-a-days, full color, use established intellectual properties ("fan art"), LGBT, and left-to-right reading. Staff are also currently featuring any series that can do a quality tipping episode, though this is likely a limited time offer.
Certain genre also do very well here at Tapastic. BL for example is something that will get you an instant shot in the arm in terms of readership. Also some genre have a smaller pool of creators, "gaming" for example. 1K subs can get you close to the top of the list whereas in many other genre many readers will never scroll that far down.
Every webcomic portal has his strengths and weaknesses. Its up to the creator to weigh out where they think they will be most successful at and apply themselves the greatest there.