I'm waiting until we get more information to make a decision (including whether I want to take the plunge of picking up a Switch in the first place), but I'm leaning slightly towards Pikachu, just because it's probably the canon version of the two. I much prefer Eevee over Pikachu, but I think it would be weird to have a rival whose ace is Pikachu, and assuming they don't evolve, I think having an Electric type will be more useful than a Normal type in the long run.