I like to choose Water Pokemon as my starter in R/S/E...but before the Water Pokemon was really weak. But now I like Piplup. But still, Chimchar it good. The trianlge is now uneven if they evolve into their final forms.
Toterra can take down Fire Pokemon with Ground Moves. It can take down Steel and Electric Pokemon with Ground Moves too. Water, Ground, and Rock are weak against its Grass moves. It can take down Empoleon and Infernape with Earthquake.
Infernape can take down Rock, Steel, Normal, and Dark with it's Fighting type. It can also take down Steel, Bug, Grass, and Ice because of it's Fighting type. It can take down Empoleon with a fighting move like Brick Break.
Empoleon can take down Fire, Ground, and Rock with the Water type. It can also take down Rock and Ice with the Steel type. Torterra can take Empoleon down with Earthquake, but Empoleon can learn Ice Beam and do Ultra power damage towards Torterra.
It all depends on the moves you teach it. Even though Piplup may sound weak, I like it the most!