We stayed at the Rio apartments quite a few years ago. They are basic - we had a studio which only had sofa beds not proper beds. If you look at the Trip Advisor website most reviews tend to suggest they need a bit of updating.
The restaurant at the Rio was very good although of course that might have changed. Pool area fairly small.
The apartments are a good 20 - 25 minute walk to the beach and the marina.
Vilamoura is a 'purpose built resort'. Lovely marina with lots of places to eat - although can be fairly expensive. It has two large beaches either side of the marina - very sandy with all the usual facilities.
Vilamoura is not the true Algarve - whilst pleasant in it's own way I much prefer the western end with its lovely cliffs and coves and stunning coastal scenery.
Pippa