For my older series it's just page by page, because that's how I've been releasing them for years and I don't really want to change up what I already have established, it would also require me to redraw a lot of old panels and pages to make them fit a vertical scrolling format (or even if I want to do any work on them in general, I use different programs now than I did when first starting webcomics). If I brought in more money from tapastic I would be more inclined to put the extra work in to make Raven Wolf fit the preferred scrolling format of the site more. For now though I can't justify the extra time and work a project like that would need (it would interfere with my current projects, slowing them down or putting them on hold).
For my newer comic I have both a page by page version No Future , and an episodic version No Future - Vertical (it's not just multiple pages though, I rework the text and panels to take advantage of the extra freedom you get with a scrolling canvas / get experience doing the scrolling format)
In concern to the comic with two versions, the page by page is a lot more popular (the page by page version has about 520 subscribers, while the episodic version has around 70), the page by page also has a much more active audience. It of course gets more updates and sees more exposure in the fresh, trending and popular sections, also brings more ad-revenue in (it's also ahead in the story BECAUSE of the page by page updates) and I find when comparing the two people like commenting on pages more than they do full episodes, (my guess is because there's less to focus on so they know exactly what it is they want to leave a comment on)
Some people just like reading it one way over the other, so exposure / add revenue aside, in regards to creation there are things I both like and hate about both, and on the reader end if people are interested in reading both versions I'll continue working on both.