Probably FF8. It takes very little initial investment to start that train rolling, and with low levels, curaga hp-junctioning, and water strength-junctioning, your limits alone will carry you through every challenge the game has to offer short of Omega, who you can still easily take down with invincibility items.

That said, the Chemists in FFV can berserk anything regardless of immunity, which is crazy overpowered, and Gau and Gogo can inflict an unbreaking charm on any enemy regardless of immunity, which may be worse, and both games allow for extremely powerful characters anyway, so the titles deserve mention, though I still don't think they are on par with FF8.