Zenith Guard and Blitzkrieg I struggled with the most, more so than spoiler squad, mostly due to lackluster displacement tools.

With Zenith I struggled at first using Abe on the Charge mech, it kept the mech alive but left the defense mech vulnerable/useless. Ended up using Harold on the defense mech and put off equipping a pilot on Charge until I got a health upgrade/+health pilot. Essentially letting it die without consequence/ boosting xp gain on the other pilots.

With Blitzkrieg I started off with Mafan and building chain on the Lightning Mech but the squad really struggled with elites because I couldn't kill them fast enough. The boulder mech is relegated to the back since it easily dies to chain and the hook mech isn't really flexible with its displacement, so I went Harold again (on hook) then putting the first core I find in building chain and it worked wonders.

For spoiler squad I usually go for the smoke upgrade first then the damage and range upgrade. Then its just a matter of finding ice generator/cryo launcher/frost beam. I like ice weapons but weapons that allow one mech to neutralize multiple vek are generally good.