The community encourage people to try out all coromons instead of basing picks on tier lists or stuff like that. Every coromons are good in their own way and none arent able to beat the game.

But, here's some of my picks for each type.

Water - Ucaclaw
Highest attack stat in the game, goes well with rain and the Splatter skill

Electric - Toravolt
High special attack, can deal some insane damage and has some priority moves

Fire - Volcadon
High special attack, paired with the fast metabolism trait its a beast

Sand - Malavite or Moffel
Malavite has a high attack stat and can be a good tank.

Moffel with the Lucky++ trait will always crits and outclasses even its evolutions

Ghost - Octotle
Strong glass canon, iirc it has the highest special attack in the game, can use giga drain to sustain itself

Ice - Bearealis
High attack, with the container power trait its guaranteed to deal huge damage. Even stronger with items boosting said attack

Normal - Armadon
Lots of coverage and a solid tank, should be able to hold his own against most opponents

I understand that there are 124 coromons in game with a reason, but I want to prepare myself to beat game on highest difficulty without any of my coromon fainting, so I have to catch only best coromons, and yes armadon is too op I beat whole game with only him in squad... he is not only awesome tank but also pure physical strenght that kills bosses in 4-7 hits.