Welcome to the forums, hope you enjoy it here
If you’re primarily looking for series with a large fanbase, shounen & seinen are probably the most popular genres. Some current examples would be Demon Slayer (Kimetsu no Yaiba), My Hero Academia & Jujutsu Kaisen. There’s also older series like Dragon Ball Z, One Piece, Hunter x Hunter & Bleach. Or Death Note & Fullmetal Alchemist (my personal preference is for Brotherhood, but sone prefer the original). But IMO the most important thing is to find series YOU actually enjoy. Since you mentioned Attack on Titan, I would recommend checking out Kabeneri of the Iron Fortress. But I would also recommend checking out other genres too.
As @sodaleaked & @efaardvark mentioned, MAL is a resource a lot of people use to find out about different series & keep track of what they’ve watched. Anime Planet can also be helpful.
Feel free to share your experiences as you explore.