For start you should always buy 10,000 box, for two major reasons:
- Premium Box cost 3 times more, but the tsums in there are not 3 times more powerful.
- When you play a game, tsums that you cleared in game will get experience point at end game, providing that the tsums are in you inventory. Aside from the tsum that you set to use, all other tsums that appear in game are tsums from Happiness Box. Therefore if you have collected tsums from Hapiness Box they will get experience point, while tsums from Premium Box won't get experience point because these tsums won't appear in game unless you set it as your special tsum.