The title says it all.
While I don’t know every Delta Pokémon at 100%, I know few good cores that may be helpful during playthrough.
Mega Delta Venusaur is simply BROKEN. By itself, sweeping all major battles become easy. Then, Delta Gallade/Gardevoir add themselves as the best Pokémon to battle Nyx. Only her Kangaskan isn’t weak to both Ice and Electric. I see many people choosing Delta Snorlax and it seems good (I guess?). Whit Thick Fat, it become neutral to Fire and Ice. His colossal special bulk allow him to conter a wide variety of special attacker and strike back.
If you get help from the another player, you might be able to put out a good New Moon team. Mega Delta Charizard as the starter and Delta Roserade and Delta Blastoise as the weather Sweeper. To counter fairy type, you have Delta Luxray that somehow everyone loves at your disposition or Delta Vespiqueen.