Never been to Denver or Seattle. But I've lived in Austin all my life and wouldn't dream of moving unless it was to Chicago or San Diego. I've been to a few major cities and stayed for a while in some, in my experience, Austin has always felt like a home to me and is probably the most welcoming city for new residents in all of the country.
living in Syracuse NY my whole life i didn't really know what to expect of TX but after visiting a good friend of mine in Austin, I feel in love with the city. Lots of awesome things to do and the culture is great. I feel like its the only city in TX i would enjoy though. Im actually planning on trying to move down there since job opportunities in my city are terrible and my job now i've kind not going anywhere.