Hard to decide between Kanto, Johto, Hoenn and Sinnoh. All of them have some great designs and/or anime nostalgia going for them, with basically the only ones I'm not that much of a fan of being Tododile's evolutions, Mudkip and Turtwig. Kanto might win on the grounds that I like all three but Blaziken and Sceptile is a hell of a duo to have. I'll say Kanto =/> Hoenn > Sinnoh > Johto