I've been to a few places in Austin and so far the only good BBQ I've found is Leroy and Lewis. They have their food truck at a fantastic outdoor area with some other food trucks, and without a doubt their food is the best in that area. I got a sampler and everything (with a single exception) was amazing! The Cauliflower Burnt Ends were an interesting concept but I didn't like them at all. The brisket was exactly what I would expect from Texas BBQ. The Barbacoa (beef cheeks) was tender and juicy, and their pulled pork was the best restaurant pulled pork I've ever had (outside of my own, of course).
Blacks wasn't very good at all...brisket was cold and dry before we even sat down. Their sides were straight food service gunk ; same stuff you'd see in a buffet style restaurant like Golden Corral or Sizzler.
I tried a few places in Killeen (about an hour away from Austin) and they aren't even worth naming / shaming.
Good luck with your trip and I hope you find some great BBQ.