I haven’t taken Delta internationally recently but as best I can tell Delta have not yet refurbished their A330s with fully flat seats. They’re almost flat but not quite. Colleagues who fly both Delta and BA tell me the food service will probably be better than BA’s on the long haul flight. BA is notoriously skimpy on the second meal across the Atlantic. But, if wine is important to you, I generally find the selection on BA superior to the US carriers. Taking DL, as you note, would allow all immigration and security to be done in Dublin. Having said that, I have had bad experience with weather delays changing planes at US airports and have been downgraded more than once on the domestic portion of my trip just to get to my destination. Also, the domestic flight ATL-DFW will be longer than the DUB-LHR flight. So you get a longer international business class flight on the BA routing.
So, the BA advantages are a flat bed and in my view a more assured connection so long as you leave enough time to connect at LHR. The cost is two trips through security (one at DUB and one at LHR). My own view is the BA lounges at LHR are still nicer than Delta’s SkyClubs in ATL.
If it were me, I would pick BA but largely because, for all the difficulties LHR presents, I personally have found BA’s connection at LHR better than changing in the US where wether delays and oversold flights make it hard to rebook in the case of delays. But, you probably can’t really go wrong either way.