Right now for new cards, the market is still cheaper to level your cards than packs. But packs have the chance of paying for themselves. If you pull one gold foil epic or legendary card worth a lot it is like you got the rest for free. So really it depends on what you want to do. Gamble and level-up cars slow till you hit a big one or just level up the cards you want on the market for a good cost per card. I mean rares for under 0.50 means a pack with one of those is a big loss. I don't suggest buying packs with 100 because you don't get the bonus save for 200 to get the free 10 packs or buy single cards if the goal is to level up.