Thread is a little old, but my top 3 are, from greatest to least:
Undertale-My favorite fictional creation ever. Toby Fox is a genius and Undertale was the first big showcase of it. I love absolutely and literally everything about the game, the gameplay, the humor, the occasional dark themes, the music, the characters, the story, the lore, the secrets, the paths, etc., Undertale is usually played for no more than a little over 10 hours at most, usually below 20. I have 111 hours in the game personally, and that's not even talking about how much content for and based on it I've seen. And the fact that the vast majority of the game was made by just one man is simply inspiring. Undertale as a game alone is amazing to me, it truly changed my life, but in addition to that, while the fanbase has some negative parts that seem to take the spotlight for whatever reason, some parts of Undertale's fanbase are amazing, notably the fan animations and fan games. There is so much I could say about why I like Undertale that it'd take hours for me to go through it all. Deltarune is looking like it might be even better in the future, as well, which is exciting.
Attack on Titan-Favorite anime of all time as of Season 4 Part 2's ending. I've heard bad things about the ending, but I'll keep an open mind and see it for myself. Attack on Titan is just incredible in so many ways. Eren is currently my favorite main protagonist in fiction, as well. Eren's writing was incredible even before Season 4, but that's when he hit his peak and people started paying attention to him more. In Season 1, AoT was amazing at selling the viewer how horrifying this world is, and also setting up another plot besides the basic one it introduced at first with Annie, the animation and music were great, too. In Season 2, it retained a lot of the horrific elements of Season 1, in addition to some new things, such as the big betrayal, and the amazing relationship between Ymir and Historia. Ymir is an amazing character. Season 3 Part 1 I initially wasn't certain on, but loved it more on the second watch, I loved how we started branching into humans being a bigger threat than the Titan's, and Kenny's entire character was amazing for me, lighthearted, scary, and went off with a pretty great message that I took to heart, and Historia was just an absolute goddess in that part. Season 3 Part 2 was easily the peak prior to Season 4, for so many reasons, I won't even get into it, but a little fun fact, Season 3 Episode 17 "Hero" was actually once rated as the best television episode on IMDb, and still has a 9.9 star rating. Season 4 is just incredible so far, for so, so many reasons. Fyi, I love social commentary.
Re:Zero-Second favorite anime, was my favorite prior to AoT Season 4 Part 2. Subaru is my second favorite main protagonist behind Eren at the moment, and in fact he's the main reason I love the show.