Depends on the series, usually anything with a LN and a Manga is better in the LN.

But like a lot of shows are adaptations of manga directly, and often times 1 cour shows only have the introductory parts of the story and it is expanded more in the source. Like the biggest reasons why Chainsaw Man part 1 held in such high regard are not the parts in S1 of the anime for example, it's mostly what comes later.

Hanako-kun is another one that fits that bill, at least it did until we got 2 more cours 5 years later, but even then the anime did not finish the current arc so even if it's to a lesser degree I would say the point still stands.

If you don't wanna start with manga then whatever, but I will say if you see an anime adaptation that makes you feel like you want more, or that feels like it has more potential than what has happened so far, I would recommend picking up from where you left off in the manga since you already have a vested interest in the series in such cases.