Board Thread:General Discussion/@comment-37293003-20181129184707/@comment-31661832-20181129185148

In general, rainbow the cards with good leader skills and the older leads that are getting EZAs (since they have a higher boost in the system). If you aren't sure which cards are good then look at one of the tier lists and focus on the ones near the top.

Ultimately it's fine to rainbow any card you use. If you use a farmable card like Eis Shenron a lot, rainbowing it is better than rainbowing some leader you'll never use.