Honestly I've tried to abandon this site a few times as far as my reading list goes, but it's the best. (My only real issue is the inability to mark partial chapters like c12.2)

The way I like to track my comics is using a lengthy personal word document. This has everything I own or have read. I give each title a rating after I finish them and I also use tags to highlight some of my favorite tropes. Each entry has a hyperlink to Baka-Updates or Goodreads so I can read a summary and related categories for each title. It would break my heart if I ever lose this document so I save a copy on my external hard drive.

On MangaUpdates, but with backups of my lists: completed and so on. Who knows what will happen to you in the next years...

I used to use MyAnimeList, but their database felt kind of limited for manga.
I've started using AniList, and they're better, but they're also missing some stuff.

I should probably just keep a spreadsheet, but the whole process of making one seems far too arduous a task.

So, I suppose I'll just continue to track the manga I've read on AniList, since there's only been a few I've read that they didn't have at the time (mostly oneshots).

I use MyAnimeList for animes and Anilist for mangas/manhwas. I also use a Notion template to keep track of my fav ones.
MangaUpdates only to see updates xD
I also use Goodreads since I enjoy reading books too.

I use to have a txt file, but then my list got too big so I migrated to mangaupdates

Honestly mostly I track things here but I would really appreciate the ability to mark partial chapters or make personal notes.

For novels I use NovelUpdates though, never tracked those here.

Two methods. First is MangaUpdates (best site, definitely). Second is my (unreliable) memory when I'm lazy. There's no point making accounts on manga sites to keep track since I read on a bunch of different sites. For anime, I use MAL - I made an account on AniDB as well but it really isn't convenient to use.

Forgot to add, NovelUpdates for novels. I'd say I like NU even more than this site, because it has hyperlinks!

MangaUpdates, of course. I've been trying to create backups by also updating on Kitsu and Anilist nowadays, but it's definitely more spotty/less comprehensive than good ol' MU.

Mangaupdates and mangadex for manga, while Novelupdates for novel mmm...

I use multiple. (So, I guess my answer is "other"? )

When I started, it was on paper, but I kept falling behind, having a hard time finding things, and such. After over six years, the issues with that method got worse, so then I finally got around to making an account on MangaUpdates. At the same time, I also made a spread sheet for finished works, a file for works which are in progress, and another for works which I want to read. Novels are listed separately, by the way, I've never created an account on NovelUpdates (I'm resisting it, like I originally did for MangaUpdates; I'll give in, eventually). After MangaDex came about, I added that into the mix.

I use MAL and Anilist for tracking manga and anime. Mostly Anilist, MAl is like backup.
I have excel for statistics (how much I read monthly and other stuff)

Tachiyomi, the browser (I migrate the browser history when I change computer or reinstall Windows) and Mangaupdates, which I update every now and then.

I wouldn't be able to survive without MangaUpdates.

Most manga reading sites has a bookmark option, no?