There is no best team unless you hack it. any pokemon can be good if trained correctly
the best team for battle dome in Pokemon emerald is a grass type(against swampert , and a rock type(against charizard and salamance)
I'd say machamp latios metagross
-Azumarill -Magnetric -Breelom -(A flying pokemon) -(a normal, fighter or psychic)
Pokemon Emerald, Ruby, and Saphire.
Blaziken, Flygon, Ludicollo, Gardevoir, Manectric, and skarmory or vigoroth