If you are there for pleasure and you can find a decent price (I have seen it vary widely...anywhere from 199 to 499 a night), the W is by far the best option. You are right in the middle of all the action, bars, music, restaurants, and the bar at the W is quite lively. The Sheraton is fine...like others said, nothing special. It is walking distance from the main part of downtown, but its a solid 10-15 minute walk and if its 100 degrees, its not that fun.

The hotels at the Domain are great if you have reason to be out there...otherwise avoid them as they are a long way from downtown Austin and traffic can be bad.

As for platinum recognition I have found it to be good at all the properties...I almost always got upgraded in some way so hopefully you will too. Enjoy! Austin is a great city.