1. Anime: Charizard, judging by the performance of Ash's Pokémon of this species in battle, which seems to be a lot more impressive than what I have seen from any other Fire-type starter Pokémon.
2. In-game: I'd say Blaziken, due to its Speed Boost Ability combined with its incredibly powerful Flare Blitz and Hi Jump Kick attacks combined with its Shadow Claw and Stone Edge for coverage, with such moves being even possibly boosted greatly in power by Swords Dance.
3. Personal preference: Charizard, due to its draconic and overall extremely awesome appearance, its ability to learn many moves of the Dragon type, my favorite of the seventeen Pokémon types, as well as the various cool abilities it can utilize in battle throughout the history of the Pokémon series; such as it being one of the most dangerous Pokémon ever in Generation II due to its access to Belly Drum combined with its high Speed and inability to be countered by Skarmory; its ability to use Fissure in Generation II, one of the coolest moves ever especially in that generation; and finally its ability to fire off absurdly powerful attacks in the Sun in Generation V, thanks to its Solar Power Ability as well as the natural boost in power that the sunlight grants to Fire-type moves. I also find the fighting style of Ash's Charizard, as well as many of the moves it can perform in the Animé, such as the Animé version of Seismic Toss as well as its other related moves such as Aerial Submission to be extremely cool.