The Valencia is without a doubt the best place to stay on the Riverwalk. If you book through Hotels.com you can usually get a room for $200/night. Well worth the price for the very high quality and unbeatable location.
I will be thrilled if we make the Big 12 Championship this year.
My understanding is that the Watermark is the nicest hotel in town.
We have stayed at La Mansion a few times and most recently a few months ago. They have completely redone it. It is a top-notch hotel now in the rooms (the rooms were not that great about 1-2 years ago).
We stayed at Valencia for the Alamo Bowl and that was a nice hotel as well (very modern).
havana inn is a great hotel with a great bar. valencia and contessa are both great choices, both nicer and newer than the havana, and both have nice lounge/bars.