Ash Ketchum started off his journey with his fabled Pikachu, and while the electric mouse mascot certainly has earned his position as Ash's trusted Pokémon, there are two other Pokémon that are debatably Ash's strongest throughout the generations. Pokémon as a franchise dedicates its time to developing Ash as a trainer along with his training methods, and usually provides a different team for him consisting of that regions starters and exclusive Pokémon with every generation. However, on the rare chance it happens, Ash tends to get Pokémon that are his strongest by training or by special transformations. Charizard and Greninja in particular take the cake when it comes to proving their strength even compared to Pikachu. However, with the two opposing Pokémon different in personality and upbringing having reached levels of strength not seen often in non-legendary Pokémon, it brings up a lingering question for many people: Which of these two is Ash's definitive strongest Pokémon?
Before Charizard and Greninja became the Pokémon they are today, they were simply known as Charmander and Froakie. The Charmander abandoned by a neglectful trainer found himself attached to Ash during its early years, and is the strongest first-gen starter that Ash has caught, proving itself strong enough in the later seasons to be a first choice for Ash in returning Pokémon Leagues as a Charizard. Froakie, by comparison, started off as Ash's first starter Pokémon in the Kalos region, further cementing the growth into a Greninja later on as the two developed their bonds of friendship and camaraderie. Regardless, both Pokémon have achieved great feats of strength and defeated significantly powerful opponents. The only question that remains with these two Pokémon is which one is debatably the strongest compared to the others, and whether the true victor goes to Charizard or Greninja.
Charizard's And Greninja's Achievements.
Ash's Charizard may not have had any mega-evolution or even the bond-phenomenon that Greninja has exhibited, but the Charizard has the advantage of being a veteran. Charizard, out of all of Ash's Pokémon in the mainline TV series and excluding the movies, Charizard has singe-handedly managed to defeat an Articuno back in Pokémon: Advanced Battle in a battle.Not only that, but despite never having achieved any Mega-Evolution compared to other Charizard, it is still powerful enough to have been a first-pick for Ash during the Unova League. Despite Charizard initially barely listening to Ash, even costing him a victory in the Indigo League back in Kanto, Charizard eventually underwent through special training with other stronger Charizard back in Charicific Valley; a valley built and made with the purpose of training Charizard's specifically.
Greninja's one of Ash's first Kalos Pokémon in that region, as well as the only known Pokémon to have developed a unique form called Ash-Greninja. While this form is a direct result of the bond between Pokémon and trainer, Greninja's longstanding bond with Ash during the entire Kalos Region shows throughout, being the ace Pokémon of that generation for the majority of the League. Not only that, Greninja certainly has managed to put up a fair climactic fight against a Mega Charizard X despite being only a starter Pokémon with a unique phenomenon of a form change.
Who's The True Victor?
With all the facts laid out pretty bare for all to see, Greninja and Charizard are very close contenders to take the top spot, being powerful Pokémon in their own right. However, if one had to give the top spot, it would have to be Charizard who has earned the right to be called Ash's strongest Pokémon. Greninja is the only Pokémon to have transformed into a bond evolution thanks to Ash and has become as signature ace for Ash in the future, but there is no denying that only Charizard has been able to defeat a Legendary Pokémon, namely Articuno. As the movies and the TV shows have constantly reminded the audience, Legendary Pokémon are strong forces of nature with powers that dwarf many individual non-legendary Pokémon. The fact that Charizard has even achieved what not many Pokémon ever get the chance to achieve puts him a cut above the rest of Ash's Pokémon, which includes Greninja even in its Ash-Greninja form.
The truth about pitting Greninja and Charizard against each other is due to the fact that both Pokémon may have an advantage over the other. However, Charizard is the only Pokémon out of Ash's group to have been by Ash's side since the beginning of Ash's journey, and the only one to have undergone specific training that forced it to grow beyond its limits. Thanks to that, Charizard has been able to defeat a Legendary Pokémon like Articuno, and made it to several Pokémon Leagues alongside Ash. When compared to Greninja, who mostly stuck around for the Kalos League and hasn't achieved too much when compared to Charizard, it's no surprise why the Fire-Flying type Pokémon earns the top position as Ash's strongest Pokémon. However, the Pokémon franchise certainly does appreciate both creatures to a certain extent, regardless of which one is the best Pokémon Ash has ever had.