I mainly do vertical format with my comic :Rebirth, and the majority of the people I know (mostly on Webtoon) are also using vertical format.
In my opinion, the pros of using vertical format is that:
- You can control the pacing a lot better. (Granted you do not overuse white space between panels, it can get really annoying)
- More detailed shots.
- Dialog don't cramp together in one page and it's easier for readers to follow. I find myself frequently skim over a lot of dialog in a normal manga page, but I rarely do so when I'm reading a vertical comic.
- Depend on person but I personally feel that the scene flow a lot better in a vertical format, like screenshot from an anime, shot by shot. If you read some good vertical comic with action (Maybe try Noblesse) you will also notice that the action scene is described a lot better than in a manga.
- Work really good in mobile format without requiring much tinkering with the panels.
Cons:
- The most prominent one that I can think of is clearly the disadvantage when you want a physical copy of your comic that is in a vertical format. I work on my comic page by page, but despite that, each page only contains around 2-3 panels, which will result in quite a lot of printed pages. I have seen other professional comics went around this problem by rearranging their panels in a normal comic format (check out Noblesse printed volumes), which I assume shouldn't be that hard but that is extra work there.
- The scrolling to read a vertical format comics might not sit well with some others, but I don't see it to be that big of a problem if you aren't overdoing your panels and white space.
- It might take you a whole episode just to have people talk back and forth while traditional format probably take a few pages since you can cramp more panels in.
All in all, to which their own, some platform prefers normal comic format (Like Tapas), while some other prefer vertical format (like LINE Webtoon), it's just how you execute the format that will either deter or attract people's interest.