I would give the edge on longer domestic first catering to AA still -- I flew BOS-DEN on DL and BOS-DFW on AA and Delta was a single tray whereas AA had a hot towel, warm nuts, and a drink to start and sorbet after the meal.

AA gives Flagship Lounge access to elites flying long-haul international. Delta is eliminating Sky Club access for their own elites.

Delta miles are easier to use for domestic flights to me, and it's nice that those flights are elite-qualifying now. I usually earn more miles than I got for my flight from the Delta 20 minute baggage guarantee.

The lack of lounges in JFK T5 is definitely an issue.