Raindrop is very good for storing bookmarks, Omnivore is pretty good at being a read-it-later app. You can annotate in Raindrop, but it's not very ergonomic, and I honestly don't even recall if it has a reader mode. I'm certainly not sure where how to turn it on on the web. Omnivore's reader is excellent and annotating documents works great.

FWIW, I use both services daily and maintain a plugin to import Raindrop annotations & highlights into Logseq. I enjoy using Omnivore for reading much more than Raindrop.