On one hand the most damaging things in MD S are barta from the mages.
On the other hand, the most annoying things in MD S are back kicks from ollakas and worm spin attacks, and jellen lols.
Well odds are you'll get knocked down anyways from the latter. If you're a force type go for the extra EVP with a mega/wall if you are unwilling to armor swap. The dfp increase will only reduce damage by a few points, but evp is more important. If you are melee then the extra EVP is kind of annoying.
Best scenario is of course to armor swap. Now that force types are buffing with defbaride or whatever it is that gives +dfp and debuffing with -atk, having good enough fire armor COULD actually make you IMMUNE to jellen. And THAT is probably the most valuable thing of all
Seeing my fortefighter take 0's sometimes from jellen attacks brings tears of joy to my eyes.
Rainbow will do nothing in regards to thunder attacks if your armor is not thunder or earth.