I have the Sally 2 wedges and love them for work. I just bought the Reva flats today so I can't speak for them yet since I haven't worn them yet. I hear mixed reviews about the comfort of Reva flats!
I think it depends on you and your lifestyle. If you're looking for a pair of casual flats that can be dressed up or dressed down then I recommend the Reva flat however if you're looking for something a bit more professional looking then you should get the Sally wedge.
If you have no preference towards a wedge or flat, I think the Sally wedges are more comfortable.
I have Revas and the Sally 2 wedges and wear them both to work. The Sallys are much more comfortable and don't bother my feet after a day at the office.
I love the Sally and Sally 2 wedges. They're comfortable, have just the right heel height, and hold up extremely well. I like the Revas too, but IME they show wear much more easily.