This is sooooooo superior to AltSpace it's not even funny. It's NO CONTEST, not even remotely. The advantage that AltSpace has is simply that they coded for cross-platform, aka that they get all the mobile and GearVR users which currently the large majority of VR users.
I really don't want to talk "bad" about AltSpace, but the few times I am still on A/S, like when there is a good music event etc and I see new people coming and being all overwhelmed, I wonder what those people would say seeing VRChat. I guess it would blow their mind. It has blown mine because it is really, really excellent. THIS alone is worth getting a Rift or Vive. (And believe me, I have seen MOST what is out there already for VR and this includes VR social apps).