Anna,
I would say that the Westin Stonebriar resort in Frisco is the nicest by far but it would be a very long drive from the weekend events. The Sheraton Grand at DFW would be best located of course and is an ok hotel. It is a little tired though. The Westin Galleria would probably be the best choice if you don't mind driving a bit. I don't like the two Park Central locations (Sheraton and Westin) at all. There is also a Sheraton (Brookhollow I think) near Market Center which is has a good location but the hotel looks pretty old from the outside. Too bad the Westin Beachwood near the racetrack doesn't open for a few more months. It sounds like it is going to be a good property.