Story mainly, if you've already beat it, do the final boss fight over and over. If you already have a maxed or nearly maxed character and parallel mission 53 unlocked you can spam that, do it offline bring 2 AI teammates, grab all 3 dragon balls real quick can be done in under 30 sec and nets 18000+ per finish, don't fight Broly, the AI are there to take a quick beating while you snatch the DB's