I'm not sure if they're the best and I know that they're not the newest buildings at Grande Vista (other buildings in the group on the same side of the lake as 79 and 84 are newer). Many people recommend these buildings because they are amongst the group of newest buildings at the resort and for their location on either side of the newest pool area, (and the Copa Loca bar and grill). It's a short walk across the bridge to the main pool area, the marketplace resort store, the Pizza Hut Express, and the activities center.
The villa units in 79, 84 and the other buildings on that side of the lake are all brand new since 2004, I think. But most of the buildings in the original sections of the resort have recently been renovated so there's not really much difference. I don't know how GV staff is handling requests for those buildings for non-GV owners now, but initially these buildings were only made available for owners.
Hope that helps.
Dick Taylor