Which is easy?

I was wondering which is easy buying 10$ worth of booster pack or leveling up your cards and moving to upper leagues. To be honest buying just a starter pack isn't enough. If you just want to play only at bronze league then it is ok but till when. Therfore you have to buy cards or purchase booster packs to move forvard. It's easy to level up your card up to 2-3 levels but after 2-3 levels it gets extremely expensive to level up your cards. The only way to level up your cards is combining cards which is same as clash royale if I'm not mistaken. But the good thing is that at least you can get free reward cards for just completing daily quests.