I would farm the higher cantina... 5k credit each match and 21 dragon balls... Sure it costs more energy but it gives more resources to things that are more important. The difference would be slim probably 1-2 days longer to unlock Kylo on the 6c.
I highly agree with Hendiju, farm the higher tier. The additional dragon balls for (QGJ?), money, ability mats is well worth it. I just finished 3 weeks of GS farming. 3 weeks, and 2 refreshes a day. I saw a total of 2, yes that is right, 2! tier 3 ability mats. Farming him actually hurt currency (1k per sim vs 5k credits from upper tier) for leveling and promotions, slowed dragon ball progression. This is why I believe we have repeat nodes of characters.
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I did some testing but they are unconclusive, maybe their drop rates are really the same. Thanks for sharing.