Booster Packs Early Game

Hi everyone! I just recently started the game and was wondering what the most effective way of spending my coins would be? I am thinking of going with gold booster packs till I reach a point where I can complete challenges then transitioning to challenge booster packs but was wondering what everyone thought was the best route of attack. I only have like 7 golds as of now and am pretty early game so was curious if I’m spending my money correctly. Thank you!