Sorry to be Baron von Poopinon, but Reason will never support VSTs. REason is designed to be an all-in-one type solution. They have no desire to support anybody else’s product. They’d probably also argue that the ReWire function is so you can work in another DAW with VSTs.
To answer the question at hand….. I’d go with Massive. It’s more of a pure synth type program, so I think you’d get more versatility out of it. I’m not the biggest NI fan, but I’ve used both Absynth and Massive, and liked Massive much more.