I'm a "both" person, really. Which one I pick is based on convenience. I'll use the app when I'm away from home, and I'll use my laptop/desktop to read any other time.
Desktop is great for larger images and traditional style comics, and gives a semi-immersive experience while phones are best for the scrolling format and suit the ADHD/binge readers or really busy reader who prefers to scroll fast through a story - not that its a bad thing, but I noticed I slow down with a larger screen, yet I can get through more comics w/o distractions on my phone, as I work on my laptop. Choices, choices, lol!
Bonus: I only watch YouTube on my phone, just before bed. Hate watching on my laptop bc it's too big, believe it or not XD