In Pokemon Omega ruby after you beet the elite four what choices of starters is there?

After becoming the Champion Professor Birch will give you the choice of choosing 1 of the Pokémon that Professor Elm gives out to new Trainers in the Johto region, they are Chikorita, Cyndaqul and Totodile.

After finishing the Delta Episode Professor Birch will give you the choice of choosing 1 of the Pokémon that Professor Juniper gives out to new Trainers in the Unova region which are Snivy, Tepig and Oshawott.

After defeating the Champion for the second time Professor Birch will give you the choice of choosing 1 of the Pokémon that Professor Rowan gives out to new Trainers in the Sinnoh region which are Chimchar, Piplup and Turtwig.