Lopez is a gem.
Also try and make sure you have a GS in the team and give them your highest crit weapon.
Toons with multi attack and high crit are good for this as well.
Multi turn full team camo is the best tool. Make sure these toons have huge or at least very high Ap weapons.
For my blues I use Dwight-Earl Sutton-Priya-Douglas-Carl. First 3 for the multi attacks, which have the potential to kill 8 walkers. Douglas with double attack weapon for the GS and heal. Carl to revive anyone who drops and give regular heal and bonus hp.
For Reds it’s Lopez(5star)-Rick(5star)-Hershal-Kapoor-Piper. Rick and Hershal ensure there is constant crit boost on top of Lopez’s lead skill. With 3 healers, unless there a toon is taken down in 1 hit the toons aren’t going down. Hershal for GS which usually goes on the 5stars 1st. Piper to stun any toon that is close and dangerous.
Greens are: Ezikiel(5star)-Margaret(5star)-Mike-James-Hershal. Margaret for crit boost, her and Hershal for heal. Hershal for Revives. Mike and James decimate walkers and Mike grants camo for almost long enough to have it locked down, only granting a turn for them to move between ARs.
Yellow isn’t really a crit team but is powerful enough to defeat almost every walker team it comes across: Camila-Raven-Charlie-Hengyen-GS Rick. Raven and Charlie clear whole lines, Hengyen grants crit. Rick for GS and regular bonus hp to weather walker attacks. Camila to help regular ARs and high damage, also helps clear stun from stun walkers.
You won’t have the same toons as me, but you get the general gist of how to form effective walker teams.