All of them, multiple times. Heck, I've gone through Johto only getting hit once (and that's only because Hitmonchan's Mach Punch automatically outsped my Espeon. Ah, those were the days). Then again, Johto is pretty easy... the first time in Crystal I got through with Typhlosion, Feraligatr, and Dragonite, all in the 40s-50s range.
It tends to happen when I get overleveled, too. Beat Hoenn with just my Swampert several times...