What is the best team for this game?

What’s the best team to defeat main characters like Rivals, Cults Gyms and E4? and not the best team to pvp or kill a certain character

shadow mega mewtwo with dark nova.

I wouldn’t keep to the same team the entire playthrough, it’s really easy to keep levels up. D. Venusaur is probably the best starter. Get the Pokémon you like that don’t completely suck (unless you’re playing on hard mode), maybe Pokémon with Intimidate or an immune ability. You can’t really go wrong (unless on hard) unless they get out-sped and one-shot by everything.
(and get an Aegislash. I can hit you up with one)

I do not know the best team but the best Pokemon(non-legendary, obtainable early) is Exadrill as it has crazy high attack stat and can ohko anything( even flying using rock slide ).
The best moveset in my opinion is-
Rock slide
Earthquake
Swords dance and
Sandstorm( Makes earthquake stronger and rock slide never miss).
Drilbur is available to catch in midna mine.

sandstorm does not change rock slide’s accuracy
why waste a move slot on something that increases 1 of your attacking moves power by 30%

Oh my bad It just never missed for me in sandstorm so I just thought that it does not.

https://www.smogon.com/dex/xy/pokemon/excadrill/