Plant is my best hero for crabs in war. If she survives, she will be able to use her white skill. Roller is similar but is more dangerous because she can destroy your midline and heal while doing it, but knock the crab off and she too will be ready to heal with her white skill. I've also done a Mega + Corgi combo, just need to make sure Mega doesn't backfire during the hero wave. And other times I just don't care and use whatever, Dwarf, Monk, Revenant.
I would recommend against Kaiju on a crab wave because there's a great chance he will outright kill the crabbed hero. Also Wee Witch. Her beam and negative healing status tend to kill whatever gets crabbed.
*I should add that we have no runes, so I don't have to worry about my super-heroes wiping my team.