There are threads for both Sheraton branded timeshare resorts on the Hotel & Accommodation Reviews sub-forum here with a wealth of information on each.
SVR (Sheraton Vistana Resort) is the original and is quite a bit bigger than SVV (Sheraton Vistana Villages). SVV is all newer high-rise buildings with elevators. SVR has some sections that are the same building layout (Cascades and Lakes) and some buildings that are newer than the older sections of SVV (development of the two properties overlapped for a while). However most sections of SVR are lower rise 2 to 3 storey buildings with walkup. It would be up to you to decide which you might like more. Personally we prefer the lower density areas where you park at the door of your villa as opposed to the high rise (and to me busier and noisier) sections.
Both properties are regularly refurbished, so that is pretty much a wash. Both resorts have sections that are newly refurbished and others that are nearing the end of the roughly 5-year cycle. I would describe the interiors of either as contemporary, with lots of stone and ceramic accents and darker wood tones for cabinets and furniture.
SVR, being the larger, has more amenities (activities and dining options) than SVV but they are spread out. So, there are 7 swimming pools at SVR to provide some choice, and different atmospheres (a couple tend to be quieter, others have popular activities for kids). SVV has 3 pools, and my recollection is that they are all pretty busy. One has a pirate ship play area in the pool which is very popular with the kids. Neither resort has a lazy river feature.
As mentioned above, access to the parks is really a wash - SVV might take at most 5 minutes more to reach the Disney parks, and 5 minutes less to Universal and Seaworld. Both have good access to the Outlets and Grocery stores - car recommended.
In choosing between the two, think about what type of accommodation you would like and what you want out of your experience. That might guide you more than when the resort was built. 'Nicer' is very subjective as the reasons why the PP liked SVV better are probably the opposite of the reasons why my family prefers SVR.