With the end of the DFW hub I haven't really flown Delta. But now that Austin is potentially a thing I'm considering it! With that in mind:
AUS-DAL and DFW (at least 6x a day)
AUS-HOU and IAH (at least 6x a day)
AUS-OKC
AUS-MSY
AUS-AMS
AUS-NRTAUS-CDG
Basically local service and then Europe and Asia directs. Plus huge frequency to each hub. AUS-MSY