Both.
I'm not too sure how the SS is. I've looked at the mech, and it looks pretty good. Almost like a dayan 3x3 mixed with a QJ pyra.
I know the mefferts is good after you break it in, but that takes several hundred solves, and it's more expensive.
So if you're a serious pyra-er, get them both, if not... Maybe wait for some reviews of the SS?