The best Pokemon TCG Pocket ex Starter deck is probably the Dark-type Paldean Clodsire ex deck, at least at time of writing, but in reality the answer is a lot more complicated than that. There are nine ex Starter decks in PTCGP that players can pick between once they complete the associated challenge missions,

In the past, Pokémon TCG Pocket has used a deck rental system where you can use certain special decks for a limited number of times. Now, Shining Revelry expansion introduced a new kind of reward that allows players to pick and choose an ex starter deck,