I think the first season was best. of course, Yankumi's way (teaching) was still fresh to me then by then, it kinda got dull after the second and third season but nevertheless it was enjoyable and worth it and I gotta say this, Season 2 and 3 was pretty much a fan service you won't resist because of the amazing cast, Season 1 too. Most especially, the third because of Miura Haruma, I can't take my eyes off him <3