I haven't stayed at either, though wandered through both. City Center (the hub for Aria) is big, lots of walking.
Aria beats the heck out of Paris for being new, upscale. Big casino. I like Paris for the shops (little interesting ones) and eateries, easier to walk outside to that side of the Strip.
Vdara's lobby is stunningly gorgeous, so I assume the rooms are also. It has a "quiet elegance" feel just walking through the lobby.
Vdara is a very short walk over to Aria, so the fact of no casino isn't such a big deal. Same card (mLife), points earned, etc. Have never seen a TR about Vdara.
Those recent MGM property offers are the most generous I have ever seen. Do Aria or Vdara just for the fact of the unusually great offers, different places to eat. May not last forever.
We loved GVR way back when they had a shuttle to/from the Strip. When that ended we haven't been back. Somebody did a recent TR from GVR. They weren't happy with the customer service, said they would never go back. Might have been a fluke.
Good luck!
Candy