Ash's Aces | Bulbagarden

So here is the thing.

Ash usually gets multiple aces during a run. Usually 2, but Hoenn has been funny in that regard, since he got 2.

The general sense also is that the mon who has the most impact on the region (So gym battle and league wise) is considered the ace (Which is funny regarding Kalos).
Kanto
Main: Pikachu
Secondary: Charizard
Johto
Main: Pikachu
Secondary: -
Hoenn
Main: Sceptile (Or Grovyle)
Secondary: Swellow
League ace: Glalie (Outperformed the other 2 at the league).
Sinnoh
Main: Infernape
Secondary: Buizel (Had more impact than Staraptor in the long run)
Unova
Main: Krookodile
Secondary: Pignite
Kalos
Main: Talonflame (Had more overall impact on the gym and league runs, since it fought 8 gym battles, lost only in 2 without taking a mon with it, the rest it didn't go down with at least taking another mon down as well and the same goes for the league).
Secondary: Greninja (While you could argue narratively Greninja was the ace, overall it had less impact than Talonflame did).
Alola
Main: Lycanroc
Secondary: Rowlet (Narrativly, Incineroar was the secondary, but overall Rowlet was, due to having had more impact on the Island Challenge and it also performed well at the league)
Galar
Main: Dragonite (Has had more impact than the secondary)
Secondary: Lucario

I am putting in Dragonite and Lucario this way, because Dragonite has done more on-screen for Ash to advance to next classes, but considering the saga isn't over yet, this can still change.

I also don't take strenght of a Pokemon into account, since then, especially Lucario has a problem for secondary ace, since currently, Dragonite (Defeated a Mega and a Champions ace, without needing a power-up), but also Sirfetch'd (Defeated an E4 member Mega Ace without a power-up) and Dracovish (Defeated a Champion mon who could go toe-to-toe with Krookodile, without a power-up) are stronger than it.

However, if we rank aces and secondaries (And Glalie) in terms of actual raw power and strenght, the ranking probably is
1. Pikachu
2. Charizard
3. Dragonite
4. Infernape
5. Sceptile
6. Talonflame
7. Glalie
8. Krookodile
9. Greninja (Ash-Greninja form would be around top 4, behind Dragonite but before Infernape)
10. Lycanroc
11. Lucario
12. Pignite
13. Swellow
14. Buizel
15. Rowlet