Ash Ketchum's journey in Pokemon has come to an end, over his 25 years on screen Ash has caught 55 Pokemon (not including 29 Tauros or some temporary ones). But for whatever reason some of his Pokemon never evolved, going back to some of his first captures Bulbasaur and Squirtle and of course Pikachu.
Ash could have had an incredible team if he chose to keep all of his Pokemon and more importantly if he evolved certain Pokemon. Considering he only had one Championship during his quest, things could have been very different if he maxed out his team to their fullest potential. There is no question about it that Ash Ketchum would have fulfilled his dream of becoming a Pokemon Master if he just did what seemingly every other trainer has done with their Pokemon and evolve them.
10 Raichu
Given how powerful Pikachu is as a Pikachu it would be a crime to omit him from this list as just imagine how strong Pikachu would be as a Raichu. Raichu just has better stats in the games, so it would just make sense that he would be better as a Raichu. The evolved form has 475 total base stats compared to Pikachu's 300, given how strong Pikachu is just imagine how much more powerful Ash's partner would be as a Raichu.
If Ash chose to evolve him during his adventures in Alola he would have an even better version of Raichu. The surfing Pokemon Raichu will offer Ash some well-needed Psychic attacks for his team. Something that he lacks.
9 Venusaur
Bulbasaur has shown throughout the anime that it has refused to evolve, but how stronger would Bulbasaur be if he could have reached his final form of a Venusaur?
Venusaur is a defensive monster in the games and this could have translated perfectly to the anime, with 100 special defense and defense. Given how long Ash and Bulbasaur have known each other this Venusaur would be insanely powerful in the anime. Having this tank at his disposal could have given him the edge in the Indigo League championship. Venusaur can of course Mega Evolve and Gigantamax which would be another tool in Ash's arsenal.
8 Blastoise
As the leader of the Squirtle Squad, there is a big reason why Squirtle did not evolve as it is not known as the Blastoise squad, however, Ash should have just evolved into Blastoise and have one of the strongest water-type Pokemon of the original 151.
Just like with Veunsaur, Blastoise can Mega Evolve and Gigantamax, so there is no question to it that Ash should have taken Squirtle to these new heights. Blastoise's design is just so intimidating with his massive water cannons, opponents would have run in fear and Ash could have gone toe-to-toe with his rival Gary's own Blastoise.
7 Charizard
Charizard has shown time and time again that he is Ash's most powerful Pokemon, whenever Ash is in a tight spot Charizard is called upon to help him out. When Charizard comes to Ash's help to take on Entei in the third Pokemon movie, the anime is at its finest.
Despite this list including some of Ash's unevolved Pokemon, Charizard still makes this list as Ash did the right thing and evolve his Charmander all the way. Even if it did take some time for Charizard to come around and listen to Ash.
6 Greninja
Greninja makes this list for one big reason, Ash has a special bond with his water/dark type Pokemon that is similar to a mega evolution. Greninja turns into Ash Greninja which makes him stronger in battle. Confirming that Greninja is one of Ash's strongest Pokemon.
Ash does not seem to evolve his water-type Pokemon, Squirtle, Totodile, Oshowatt, Buizel, and Corphish all remained involved but for whatever reason Ash evolved his Froakie, and it returned to him tenfold. Greninja has one of the best designs in anime and this red coloring edition with this bond with Ash makes it even better. Deserved a place among the strongest of Ash's Pokemon.
5 Dragonite
Fans of the series thought that Ash's chance to get the original Pseudo-legendary of Kanto was long gone but in Pokemon Journeys: The Series which took place mainly in Ash's homeland he captured one of the strongest Pokemon from the original 151.
Dragonite has shown throughout the series that he is so strong and takes his place in this team rightfully so. Dragon-type Pokemon have a certain specialty about them, and it is a real surprise that it is currently the only pseudo-legendary in his possession and just his fourth Dragon-type overall.
4 Tyranitar
Although Larvitar was not actually owned by Ash it did hatch from an egg in his care and travel with him for some time before he left it in its care with its mother Tyranitar on Mt. Silver.
Ash should have jumped at this chance to have another Psuedo-Legendary Pokemon and claim Larvitar as its own and eventually evolve it into the powerhouse that is Tyranitar. One of the best designs in Pokemon and there is no doubt that it would have made a powerful addition to the Pallet Town trainer's roster. There are questions as to whether Larvitar was officially his, but he is regularly seen in flashbacks showcasing all of Ash's team cementing the fact that Ash did technically own Larvitar.
3 Garchomp
Fan-favorite Generation 4 Pokemon Garchomp could have been Ash's if he evolved his Gible, the design is just incredible, and he has the power and abilities to match this. Champion Cynthia's ace is a Garchomp and Ash could have had a direct counter to this with the dragon/ground type of his own.
Ash really dropped the ball with this one, Garchomp is another pseudo-legendary and a monster with his powerful STAB Draco Meteor and Earthquake. He could have decimated the Sinnoh League and claimed another championship for his belt. Why Ash? Why keep this one as a Gible?
2 Solgaleo (Nebby)
Just like with Larvitar, Ash did not technically own Solgaleo (nicknamed Nebby), he did however raise and care for it as a Cosmog, through to Cosmeon, and eventually as a Solgaleo. Ash and his Legendary Pokemon parted ways, but again another poor decision from Ash as he could have had a Legendary Pokemon to call his own.
Partnering with the last Pokemon on this list then Ash really would have been unstoppable in Alola, more so than he already was. Solgaleo's powerful Sunsteel Strike is its signature move and opponents would have quaked in fear at Solgaleo and Ash, but he decided to let another powerful Pokemon get away. Some Pokemon Master Ash is.
1 Melmetal
It comes as no shock that Ash won the Alola league when it was the first time that he had a Mythical Pokemon in his team. This is without a doubt the strongest Pokemon that Ash has on his list. It really is a surprise that he decided to keep his Meltan as Ash tends to let his strongest Pokemon get away and then when he does have a strong Pokemon he decided to keep them unevolved.
So it is a massive credit to Ash, not only did he keep a MYTHICAL Pokemon, he actually decided to evolve it and unleash its full potential. If only Ash had the brains to do this to all of his Pokemon then he really would have become the Pokemon Master.