The soundtrack from the new BattleTech PC game seems to fit pretty well. Just the right mix of hope, desperation, high-tech and low-tech, especially in the main theme.
https://www.youtube.com/watch?v=AjS7xfX ... 4HECPKusy3Otherwise, pretty much any of the Gundam series' soundtracks can work pretty well depending on the mood you're going for. Which is one of the great things about MFZ, it can have just about any "feel" to it that you want it to, all depending on the story you want to tell and your actions as a player.
For over-the-top and/or silly/dramatic games:
https://www.youtube.com/watch?v=Ws3kY2LNPbM (Lots of

-using frames advised, if not downright necessary.)
For more serious battles that still have an element of heroism:
https://www.youtube.com/watch?v=b40mZVnQCTsFor games that are even more serious, to the point of being downright gritty: !https://www.youtube.com/watch?v=t1zJKECM_0s (See advice for G Gundam)
For tense covert-ops type battles, or intrigue:
https://www.youtube.com/watch?v=yuLLRdsGNJo (Especially useful if one side has swarms and the other has a few maxed-out frames.)
For when the fates of interstellar nations are hanging by a thread:
https://www.youtube.com/watch?v=kKCCNMyKNJcFor that first moment when a frame launches in a story, or for "zooming out" and surveying the battlefield and reflecting on the cost of victory:
https://www.youtube.com/watch?v=fJNMfDi ... 6EF669F49CAnd for general purposes/use as a theme song:
https://www.youtube.com/watch?v=Y-0_s2_QR8oAnd those are just the ones I think of off the top of my head!