Sooo, E6 Pela or E1 Welt?

My current team is Acheron, Gallagher and Guinaifen, and i couldn't decide if i wanted Pela or Welt in the last spot. Pela has her cone S5, and Welt has his in S2. What do you guys thing it's better? Pela's defense reduction or Welt's multi-target slowness effect?