Let's analyze that statement.
Roark: Can be bested by all three starters.
Gardenia: Chimchar has the advantage. Turtwig is neutral. Piplup is bested here.
Maylene: No one really has the advantage here. If Prinplup has Peck, he'll kind of have an easier time.
Crasher Wake: Grotle's got the upperhand.
Fantina: Nobody really has the advantage here, either.
Byron: Infernape and Empoleon have the advantage, but Torterra isn't too hateful, either.
Candice: Infernape has the advantage. Torterra fails. Piplup is neutral.
Volkner: Torterra. has the definite advantage here. Earthquake will cream Raichu and Luxray, and electric attacks have nothing on him. Infernape is neutral, and even though he's part Steel, Empoleon fails. :x
ELITE FOUR:
Aaron: Torterra won't be very useful here, but neither will Empoleon.
Bertha: Empoleon and Torterra can both beat her, and quite easily, too.
Flint: Empoleon wins here, but Torterra can Earthquake Flint's team without getting hurt too badly by Fire.
Lucian: Nobody wins here, really. Infernape, however, loses.
Cynthia: Each starter can own at least one of her Pokemon, so it really doesn't matter much :x
So let's tally.
Turtwig and Evos: 4
Piplup and Evos: 5
Chimchar and Evos: 5.
So technically, Turtwig is the worst. If you're thinking type advantage. However, when thinking stats, Piplup still has a crappy stat total and movepool. :\