This is timely, today I booked 3 nights at FS Austin for an early summer family wedding. I was looking at the other 3 "upmarket" properties you mentioned as well. Because of their 3rd night free promotion, FS was actually the cheapest of the four.
I've stayed at The Driskill and W. The Driskill is interesting but doesn't have a pool which I require in Austin summers. The W actually wasn't too bad, I really like the location, and the spa services were quite good. I did not care for the pool and had an average meal at the restaurant.