Up to you. If MT is dear to you, then you may want to minimize Contracts cost. 1 game for a Gold is 48MT, but only 20MT for a Silver, and a miniscule 8MT for a Bronze.
What I've done, more or less, is play with the "worst" lineup that I still feel like is good enough to guaranty that I can win. Lately, into the second half of Historic Domination, that has been 3-5 Golds and the rest Silver. I don't bother with saving the difference between Silver and Bronze contracts, only between Gold and Silver.