Manga or anime?
The anime is fine, although it covers the worst arcs, so you might as well read the manga only.
Manga. Anime is pretty weak. Just watch the special episodes at the end of each season . Specially the second season one. But wait until you've read the manga to watch it.
anime doesn't have the Minus arc
alternatively you could watch the anime and continue with the manga
just start reading after the flask plan arc. where the anime stops
Oh, and don't drop the manga before you get to the minus arc (starts at chapters 55-56). You might stop enjoying it at times but it will be pay off latter on.
The anime was a pretty good adaptation considering what it covered. The first season was crap, and the second season was somewhat good - just like the manga.
Don't even bother with this piece of shit at all.
Manga to understand more about the story, anime for this.