To me, it's simply which resort and which location you like more.
I would not worry in the least about re-sale value down the road -- Riviera is now 2 years old, resale value has been consistent with other resorts, in terms of proportion of direct pricing. (a resort with direct pricing of $250 per point will have higher resale value than a resort with direct pricing of $190 per resort). In fact, as soon as the new VGF direct pricing was announced, re-sale prices of VGF have plummeted, and are now about the same as RIV resale prices. And with the longer contract, Riviera may ultimately retain better resale value, depending when you sell. 40 years from now, Riviera will likely have far better resale value -- As Riviera will have 8 years left, while GFV will only have 2 years left. So, in the end, I just wouldn't make resale value part of my decision at all.
Both resorts offer larger-than-average rooms, they both offer elegant high quality decor. Whether one prefers the style of one over the other is purely subjective and personal preference.
If you prefer a monorail / Magic Kingdom location, then VGF is better..
If you prefer an Epcot / DHS location, then Riviera is obviously better.
Apart from location, I'd say a big difference is general layout -- Do you like a big spread out resort, may prefer the style of VGF.
Do you prefer a smaller more compact resort, where you're never far from the dining, never far from the pool... Riviera is a better choice.
Finally, somewhat speculative -- There is a chance, that it will be easier to get larger non-studio rooms at Riviera, as the new expanded GFV may not have enough larger units. But this is highly speculative.