The Pokémon: Advanced Generations (titled Pokémon: Ruby & Saphire in Japan) was the direct sequel to the US's original Pokémon series. It covered seasons 6 through 9 of the series, each with their own respective titles: Season 6 Pokémon: Advanced, Season 7 Pokémon: Advanced Challenge, Season 8 Pokémon: Advanced Battle, and Season 9 Pokémon: Battle Frontier.
Throughout the entirety of the series, Ash caught new Pokémon that were exclusively found in the Hoenn region (which is where the series takes place. Although he used many Pokémon from the previous series, he didn't use them as much as the Hoenn Region Pokémon he caught while traveling. Many of these Pokémon are considered some of Ash's strongest throughout his journeys, while others didn't make much of an impact, despite becoming fan-favorites throughout the series. Note that only the Pokémon with more than two battles will be included, plus those caught in the region. Here are Ash Ketchum's strongest Pokémon in the Pokémon: Advanced Generations anime, ranked by win rate.
7 Sceptile - 61%
From first getting caught in Tree's A Crowd as a Treeko, Ash's Sceptile became a fan favorite for fans of the series. It's one of the four Hoenn Region Pokémon that remained with Ash throughout the entire Pokémon: Advanced Generations series. Despite being known as one of Ash's strongest Pokémon in the series, Sceptile's win rate is actually the lowest of his Hoenn Pokémon, with 28 Wins out of 46 Battles. However, it should be noted that it's third place in having the most battles out of any Pokémon on this list. Sceptile also ranks high as one of Ash's strongest Pokémon he has ever caught during his journey.
6 Torkoal - 65%
Not joining the team until Pokémon: Advance Challenge, after the group saved it from a group of Steel-type Pokémon, this adorable Pokémon may not look like a threat, but it can pack quite the punch. Torkoal became Ash's only Fire-type from the Hoenn Region. It's fought fewer battles than most of Ash's Pokémon since it only appeared between Pokémon: Advanced Challenge and Pokémon: Advanced Battle.
Counting its loss in Pokémon: Battle Frontier (which was its only appearance in that series), Torkoal has a total of 11 Wins out of 17 Battles, but still has more battles than Ash's Glalie and Donphan combined. That's quite the feat for a Pokémon with the motif of a turtle.
5 Corphish - 67%
With the most Wins of all of Ash's Hoenn Pokémon and second most Wins in the entire series, Corphish is the only Water-type in Ash's team while in the Hoenn region as during the Battle Frontier league. It was Ash's third wild-caught Pokémon while in the Hoenn region and another fan-favorite of the series. Aside from Sceptile and Pikachu, Corphish was Ash's most commonly used Pokémon between Seasons 6 ad 9, with a total of 32 Wins out of 48 battles, which is more than Sceptile. For such a tiny Pokémon, perhaps it's understandable that it has won more than other Pokémon.
4 Swellow - 68%
Swellow deserves more credit than it is given since when it was first encountered as a Taillow, it challenged Ash and Pikachu to a battle and was able to take multiple Thunderbolts from Pikachu, which usually nocks a Pokémon out. Its number of battles is within the median range, but the most it ever lost was once in both Seasons 7 and 9. Swellow's Win to Battle rates is 17 Wins out of 25 Battles, making it one of ash's more formidable Pokémon, considering it stuck around throughout the entirety of Pokémon: Advanced Generations. It was quite the loyal Swellow to Ash and helped him throughout many tough battles.
3 Glalie - 75%
Glalie is Ash's first Ice-type Pokémon. Having first joined Ash's team as a Snorunt, Glalie only appeared during Season 8, Pokémon: Advanced Battle, before being sent to Professor Oak's lab as Ash went off to face the Battle Frontier.
Glalie is technically Ash's Hoenn Pokémon with the least number of wins throughout the entirety of the Advanced Generations series since he only appeared for one season. But with 6 Wins out of 8 Battles, its Win-Rate is higher than both Corphish and Sceptile.
2 Donphan - 88%
The Pokémon with the second most Win-Rate throughout the Pokémon: Advanced Generations series, Donphans success is sadly due because it only joined the series in Season 9 Pokémon: Battle Frontier. Much like Glalie, its one-season appearance allowed for a higher Win-Rate percentage. It first joined Ash and his friends as a Phanphy after hatching from an Egg while Ash traveled through the Johto Region. It later re-joins Ash and evolves into a Donphan, gaining 7 Wins out of 8 Battles.
1 Pikachu - 91%
As the Pokémon franchise's mascot, it's no surprise Pikachu is the Pokémon with the highest Win-Rate in the Pokémon: Advanced Generations series. It's been with Ash longer than any other Pokémon throughout the entirety of his journeys, and the one with the most Wins and Battles in the Pokémon: Advanced Generations series. Its experience due to its long time with Ash, and allowed it to stack up 86 Wins out of 95 Battles while Ash explored the Hoenn Region and the Battle Frontier. Pikachu is perhaps the strongest Pokémon Ash has in his arsenal, despite not being evolved. This is quite the feat of battles Pikachu has experienced, so it's no surprise that Pikachu is considered the best trump card during Ash's many battles throughout his journey.