I've read/watch lots and lots of manga/anime respectively and my top 3 based on different aspects for both would be:
Manga: 1. One Piece, 2. Shingeki no Kyojin, 3. Magi/Nanatsu no Taizai (very close).
Anime: 1. Guilty Crown, 2. Steins;Gate, 3. Kyōkai no Kanata.
*Highly recommend you to check out those series if you don't know them ^^.