For me, definiely the Revolution, and probably a PS3 after a while, when the price drops and more good games are available. Nearly all of my favorite games are for old systems, so backwards-compatibility is my primary consideration. Being compatible with Cube games right out of the box, and emulation of older games also being made available (no more having to play illegal ROMs or paying an arm and a leg for hard-to-find games!), I think that's a winner right there.
But again, I'll also have an eye on the PS3. There's some stuff on there that interests me.