WiFi wise, Infernape as it can be used for many purposes such as Physical Sweeper, Special Sweeper, and even a lead Pokémon for the team. Its stats are quite high in speed, attack, and alright in Sp. Atk, which is why it is mostly used over most. charizard happens to be another strong starter as he can learn a variety of moves and can be a great special or physical sweeper depending on the person's preference.
A third starter who I think can be quite strong is Swampert, not only because of its stats, but also because of its different array of uses. As it can be a great lead, or even a nice defensive wall. xD