>>47545906It really depends on what team is being made. When it comes to competitive, it's balancing good type synergies with mons that can tackle the highest tier threats with an aim to cover each other weaknesses, especially with defensive cores such as Ferropex.
For Monotypes it's decided on what you're doing, since competitive is all about focusing on a playstyle and having good balance within it and for casual it's about offensive and defensive checking for weaknesses as well as strong gamesense and knowledge, in which I always try to get at least two mons that can take neutral hits from the common weaknesses the type has.
For basic casual gameplay, the strongest basic team to go for is a Grass-Fire-Water core, but it can vary based on the starter/team being built and what needs to be tackled the most for good balance. If I were to choose, it'd likely be:
Fire, Bug, or Flying
Grass and/or Electric
Water
Physically based type (Ground, Rock, Steel, Fighting)
Specially based type (Ghost, Psychic, Dark, Fairy)
Any additional type to round out the previous members
