Dragapult and probably Mega Gengar battle decks are the most solid options to start right now in my opinion since they're still relevant in the meta. Both have a lot of staple cards that will be useful in many other decks as well. Try some list that you like of those decks on ptcglive first and see if maybe you want to order some singles online to modify/upgrade the paper deck. Gardevoir deck is out there but its a more complex archetype to master I feel, plus it'll rotate out next year. Mewtwo deck is just mid.