I hope Ash to catch Psychic and Fairy type Pokemon. I know Ash has Mr. Mime, but it is mostly taking a role as housekeeper. So, I want Ash to have Psychic/Fairy type Pokemon which he can actually use it for battle.
The Fairy Types are a difficult choice, considering most of them are too "girly". I have a few candidates, though:
+ Togepi/Togetic/Togekiss: Back in Kanto, Ash was who founf the Pokemon Egg from where Misty's Togepi was born. Since Togekiss is a Pokemon that can use Aura Sphere, just like Lucario, it might work for Ash.
+ Zacian: During the Darkest Night, it was obvious Ash and Goh created a bond with Zacian and Zamazenta. Goh expressed interest to capture Zamazenta someday, so why wouldn't Ash capture Zacian too?
+ Galarian Weezing: Back in Kanto, Ash already used a Weezing once and won a battle; so it would be fitting for Ash to capture a version of this Pokemon that have the Fairy Type.
For the Psychic types, there are several candidates:
+ Orbeetle: Between the Galar Pokemon that Ash might capture in the future, this is a good candidate.
+ Alola Raichu: We have already saw Ash using a Raichu without evolving Pikachu, and since this regional form has the Psychic type, I believe it is a good candidate. It could also be a Raichu evolved from a Pikachu knowing the more Surf.
+ Mewtwo: Mew has become the endgame for Goh, and if he actually manage to capture, then I believe Mewtwo MIGHT be capture by Ash. On one hand, we know Ash and Mewtwo already share a bond; and on the other hand, I don't see why they have brought Mewtwo back into the anime after so many years if they don't have a plan for him. Ash could even give him the MegaEvolution X, becoming part Fighting Type.