This is a tough one. If I was recommending anime to someone brand new to anime then there are a few guidelines I'd follow:

• Can't take too long to develop. So while things like Frieren are undoubtedly amazing, the slow start means I wouldn't recommend it to a Newbie.
• Must be palitable for a wide range of audiences. Panty and Stocking, Elfen Lied, and Devilman Crybaby might be a great shows but they're pretty in-your-face and could be off-putting to people.
• Must be easily digestible. One Piece might be a great anime but no one is going to want to start on a series with over a thousand episodes. Likewise stuff like Serial Experiments Lain and Evangelion are good but far too out there for a first timer.

To that end I usually start people with Your Name. It's movie length so easily digestible. The animation is beautiful. The plot is relatively unique while still being easy to understand. And pretty much anyone can enjoy the mix of slice-of-life and supernatural.

I've also had a lot of success with Ouran High School Host Club. Everyone can understand the concept of a school but then the inclusion of the wacky rich people makes it a fun time. Another school slice-of-life could work here too like Toradora or Azumanga Daioh.

Finally, back in the day I got a lot of people into anime with Beck. It's still pretty good even by today's standards but another anime about music or a band would also work since people tend to understand music or band dynamics in general. Possibilities include K-On or Your Lie in April.

Anyway, just my thoughts.