when i was a kid i watched so SoSO many animes on TV (like Pokemon, DBZ, etc) so...
the first one watched online (internet) Is Nanatzu No Taizai (The seven Deadly sins)
but i hightly loved and recommended is Kyoukai No Kanata (Beyond the Boundary), The serie, i don't see the manga but i think its the same story
On TV, obviously Pokémon, but for streaming anime, my first was Kill la Kill, which I watched close to release. I've only had the time for like eleven other animes ever since, but it's all been great.
Pokemon Indigo League with the epic latin spanish dub on TV, but being honest with streaming it was Mirai Nikki and now I realize that it's bad than the first time I watched it.