Depends what else needs maxing in Lab, if you have maxed out all the elixir upgrades I would go minions for sure as they would help you get more DE if you moved up to a good range for DE and used BAM, instead of using it where there is scarce DE.
ill add that I just went to TH9 with a level 10 BK and level 3 minions, I would have preferred to have a 9 BK with 4 minions but I used up too much time in lab upgrading Pekkas to 3 and I don't even use them other than to mess around.

