Definitely Lady Bird Lake. It's on fire right now! If you can swing it and he's available, hire Charles Whited (Barefootfishingtours.com) as a guide for a day. He's had some monster bags out there lately and he can definitely put you on fish. You could catch the fish of a lifetime there right now.
"If people concentrated on the really important things in life, there'd be a shortage of fishing poles." - Doug Larson