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,

The developers of Pokémon TCG Pocket released Charizard ex as part of Genetic Apex booster packs when the game launched in the fall of last year. Since then, we’ve gotten several expansions that have introduced strong cards like Arceus ex, Dakrai ex, and Sudowoodo (if you can believe that).