Arcane. But I'm pretty sure Arcane will be the best visual media I will ever see in my lifetime that nothing will ever really compare to, so it's probably a good thing it concluded while at its peak.
Fringe was at it's best during their earlier monster-of-the-week seasons but quickly strayed away from that to progress the overarching story, would've been nicer to have more seasons with a slower burning story development while still focusing on what made the show special.
Legion (FX Series) while excellent on it's own, you could tell the productions creativity was far from exhausted and could've easily filled another wacky season.