TLDR: Ubooquity is king imo for in-browser reading. Kavita is simple & looks good. Calibre + Calibre Web is most advanced

Calibre + calibre web is the best combination. Calibre itself is very powerful and Calibreweb makes it fine to look at. I had 2 issues that pushed me away from Calibre. First is that my ebook library isn’t in the “Calibre” format, so I’d have to import all my ebooks … which essentially copies them to another directory in the layout Calibre wants. Ik know ebooks don’t take up much space but i don’t need a duplicate of the entire library. Second (in line with the first) is that i don’t want to import every new book manually so that Calibre can interact with it.

Currently I run Kavita and don’t have any issues with it. It works fine, and looks good. Not sure what features you are looking for, but i feel most of peoples needs are satisfied by Kavita.

I will say, i don’t read books directly through these services. For that I use (and absolutely love) Ubooquity. I use Kavita to easily send books to my Kindle. If that is also your use case you’ll have to set up the email stuff which can be annoying but is well worth the effort.