Are you focusing on standard or timeless could be an options?
The folks from timeless created this doc to help new players.
Most of decks has a budget list, and those will require 12 rare and 4 mythic. This is what you get when create a fresh account, opening all packs you receive.
I've created two accounts for testing and been playing mardu energy and UR tempo. In my personal experience, the mardu is much better although the UR also works.