Ok well, there's two sites I use, myanimelist.net and anime-planet.com
Pros: Anime-planet is alot more easier to use and you could share how much time you've spent on anime or manga/manhua/webtoons
But it doesn't show you the day you finished the Anime, that's the only con about it. It does but only for a certain amount of time, like if you finished a anime back in 2015 Aug 22, you would have to go to your feed, and go through every single anime that youve watched, updated, want to watch, and search for it till you find it and it would probably just say (Aug 2015) And it will only do that on the day you update the anime you are watching (Like saying you watched 9 out of 12 episodes) or you completed the anime.
On the other hand, myanimelist.net is a bit harder to use because you have to know how to basically use bbcode but i learned how to use it in a hour. If you already watched an anime form awhile ago and know when you watched it, no worries, you can just put it as "completed", then rate the anime if you want like (10 out of 10 or 1 out of 10), then you just insert the day you began watching it then when you finished it. Plus it has a great community where you can join clubs and forums to get stickers or stuff like that.
On both sites there are challenges like "2018 Anime Watch Challenge!" Anime-Planet is alot easier and not much of a challenge just more of a "Lets look what they recommended me to watch" then theres myanimelist where it takes more work. You have to sign up on the forum (you dont have to make a forum account since its basically made when you make your account but you basically have to sign up for the contest and post it on that forum post) The challenges are much more of a challenge like "Watch a anime that started airing from 1990-1999" or "Watch a anime that was favorited on this site 5 times" (which normally means the anime is new or bad so gotta be quick). Its a hassle to update your challenge list and stuff like that you gotta like bookmark the page you post your reply to the challenge so that you can get there quickly through the mass heaps of people joining the challenge which will last from January 1st to December 31st this year. You can also choose the difficulty of the challenge (which i believe is noobie which is 15 anime challenges or something). You also earn a banner or get to use one while participating and if you complete your anime challenge.
Thanks for reading, i know this may have been very confusing but i'm very passionate about anime and these sites then I really like being organized with my anime especially the days when I watched them. ( I find the information useful)
If you would like any recommendations for manga/manhua/webtoons or Anime (Watched over 6000 episodes and completed 210+ anime) then just message me. If you want to add me then just go to:
(Btw still moving my list from anime-planet to myanimelist aka MAL)