Arryn is already a champ in Paldea, tho she just uses the Terastal phenomenon to level the playing field.

Avian... out of all the pokemon he's collected over the years all of them serve a different purpose for different tasks so there isn;t an "ultimate" team. Though if he had to pick out of 6 out of the ones he has:
Charizard (kind of a mandatory pick as his lifelong ace and friend)
Silvally (Water Memory)
Roserade
Togekiss
Espeon
Dragapult