If you don't mind reading on an app, Tachiyomi is the most complete of them all: by itself it's not much, but once you go to the browse tab and download some extensions, you basically have to your disposal all manga you will ever imagine. Mangadex, Manga read, mangasee, comics... All of these websites, and many more, are available as extensions in Tachiyomi.

Mangadex is the best online reading experience I've found. Use a unique random password with the site, they've had a plaintext password breach in the past.

There are a near infinity of those out there, many of which just grab other scanlation groups' output and slap their ads on top of it.

Mangadex is generally my happy place, but you'll have to wander out and about for various specific mangas.

Several of the groups that post on Mangadex also have their own website and you may find more stuff there.

For example right now I've landed on asurascans.com, which has a bunch of Korean and Chinese long strips, with generally good quality translations.

The usual sticky points with all those manga sites is the ability to track where you are in a series and continue where you left off when new chapters are posted.
Even Mangadex struggles with that, their "Updates" page is the closest thing they have to doing that and it's still not very good.

If you're going to stick to one site for any length of time, and you happen to be comfortable with userscripts, Id' suggest you head over to greasyfork.org, search for the manga domain you're using, and look for scripts that might improve your binging experience there.

Nyaa?

Install Tachiyomi and then you can use lots of websites like MangaSee, Mangadex, Nhentai, AsuraScans and many more.

You can get by with just the tachiyomi app on it's own as it has multiple sources built in, but I run FMD to automatically scrape for series I follow, that downloads them, compresses them with jpg if needed, packages them into a standard CBZ file, cleans up the filenames then those files are picked up by Komga for management and metadata, which does have a web reader that works fine (and if you use it on multiple devices it keeps track of where you are up to in a series), but also can be connected to Tachiyomi to read from, though you lose the cross device tracking if you use a third party app.

mangareader.to

comick.fun is the website i use for all my manga, you can even install their website as an PWA

If an app is ok - Kotatsu

mangasee123 has good quality scans. although their collection isn't as vast as mangadex, you can rely on them to get the best manga qualities.

If you want official translations unlike mangadex which are fan translations (not saying they are bad but could depend on what you’re reading). I use mangapill to read as pretty much everything on there is official English translations and you can also read it online.

nhentai