I tried Kavita first before moving over to calibre-web. Just with ebooks, no comics, the user experience in Kavita was a bit confusing (i.e. the way they reference books/series etc). Calibre-web does a much better job with ebooks imo. I will say the UI in Kavita is really nice. I have a Readarr->calibre->calibre-web stack, so Readarr/calibre takes care of organization for me, Calibre-web is essentially just a frontend to download and send to kindle