I think season 6 is the best season. A lot of my favorite episodes are from that season, including the (in my opinion) best episode of gumball, that being "the parents". Really, I just think the later seasons (4-6) are the best parts of the show. Not saying that the earlier seasons are bad, season three is probably my second favorite, but compared to the latter half, it's no competition. (I would rather count season 1 as separate from 2 and 3 because it's so different)