According to data from the popular anime listing website MyAnimeList , the first episode of Shingeki no Kyojin: The Final Season was the most-watched premiere among the site's users. As of Monday, 144,668 users had the anime listed as "watching" on their accounts, surpassing the third season of My Hero Academia , which had recorded a total of 107,042 viewers.
In response, MyAnimeList noted that spam accounts are being counted in the rankings, but still, Attack on Titan The Final Season is still the number one premiere, even after discounting all users who listed the anime with a "1" or a "10" in the rating portion.
The final season of Shingeki no Kyojin premiered on December 7th.
Source: ANN