I start
no mega predictions for now, maybe its mewtwo Y maybe its mega TTAR who knows but those are not in my prediction list
ok hear me out, cards like Rainbow cave are not here, because its not specific made for dragons, it works in fire decks and even some dark decks etc. and probably more in the future, so its excluded. same for all the pokemon specific supporter like Cynthia, Fantina, brock etc.
its just to give you an overview of which types have the most generic support with trainer cards. while water has the highest amount of cards, grass is the most complete one that lets you run all of them in one deck most of the time.
EDIT: no drayden included for the reason that it cant be used with all dragontypes in the game, so its too specific and i left it out. i forgot fishing net for water and electric generator for electric type.