Note: These are in no particular order. If the shows are still running, the stats are as of the writing of this article.
1. Gravity Falls
Plot: Twins Dipper and Mabel Pines are sent to their great uncle's tourist trap in Gravity Falls, Oregon. Quiet as it is, Gravity Falls has a roster of quirky citizens. However, this town is not what it seems.
How to Watch: In order. Don't skip a single episode. At the end of the credits, there's what looks like random letters. Try to decipher them using a whole bunch of methods.
2. Little Witch Academia
Plot: Despite not having any magic blood, Atsuko "Akko" Kagari attends Luna Nova, a witch school famous for teaching the once illustrious Shiny Chariot. There she finds not only Chariot's staff, but a whole lot of adventure.
How to Watch: In order. There are filler episodes, so skip those.
3. JoJo's Bizarre Adventure
Plot: JoJo's Bizarre Adventure follows the Joestar lineage from late 1800's England to late 90's Japan (and that's only the anime). Each generation must face their own otherworldly opponent with only wit and magically ghost things (called Stands).
How to Watch: In order. It's best if you don't skip episodes, but if you have to it's fine.
4. My Hero Academia
Plot: Izuku Midoriya is a powerless teenager in a world where nearly everyone has their own powers. Despite this, he is still going to apply to the best hero school in the world, UA. His superhero idol All Might encounters Izuku and promises to train him. Things only spiral out of control from there.
How to Watch: In order. Try not to skip episodes.
5. Avatar: The Last Airbender
Plot: Water. Earth. Fire. Air. Only the Avatar, master of all four elements could bring balance. But when the Fire Nation attacked and the world needed him most, he vanished. A century later, Water Tribe siblings Katara and Sokka discover the Avatar encased in an iceberg. Together they must defeat Firelord Ozai and restore balance.
How to Watch: In order. Trust me, you don't want to skip.
6. Spongebob Squarepants
Plot: Spongebob Squarepants is a frycook who lives in the underwater town of Bikini Bottom. Lots of stuff happens.
How to Watch: In any order. The general consensus of the internet is that the only good episodes are from seasons 1-3. Everything afterwards has been a decline in quality (I'm going to have to agree with them on that).