I think this depends on the intended audience. My answer would be different depending on if I am talking to somebody familiar with the anime landscape vs somebody not familiar with anime. Trying to keep things generally spoiler-free below…
For the anime-initiated
Fullmetal Alchemist (not Brotherhood) - I know, this makes me a terrible person, but I actually like the anime-original ending of the first Fullmetal at a conceptual level. It raises a lot of questions about the nature of alchemy and how it is inseparable from violence. You can really read a lot into it and apply it to things irl.
Usagi Drop - The manga has ruined this series for many, many folks in the greater anime community. However, just taking the anime as a standalone piece of media, Usagi Drop is a great series.
For casuals
The 100 Girlfriends Who Really, Really, Really, Really, REALLY Love You - The title of this series makes people think that this is just some trashy, fan service filled, harem trash…which it kind of is. But, at the same time, it is actually hilarious and quite touching a lot of the time. The premise is ridiculous, but so is how much effort they put into making sure that it is executed to perfection.
Reincarnated as a Vending Machine - Another series in which the title makes it sound incredibly stupid. However, I enjoyed this show a lot and it was way better than I had thought the premise would allow.
Rascal Does Not Dream of Bunny Girl Senpai - This is a series that I have recommended to people irl before and gotten some weird looks in return after they hear the title. In reality, this is a great series that uses supernatural occurrences to explore the insecurities and difficulties that arise as children grow up.