Hut's is one of Austin's favorite places for hamburgers. This place is always packed, though, so beware of long lines and finding parking. If you're gonna go for it, though, my suggestion is to get there before the crowds. I've gotten there at 11 AM for lunch and by 11:30 there were only a couple of tables left. It's definitely a busy place but their selection is worth it.
Make sure to check their menu online if possible because the variety may overwhelm you, specially if you're hungry and have been waiting for a while. They also shakes and plate specials. Make sure to check the back of the menu to check their daily specials. They always have something going on.