I did ATL-EZE in J last December. Standard DL international BE experience. ^

The a/c used are the same 763-ERs that are used on DL transatlantic service. No, the Y seats are not spacious, but no more so than any other major carrier.

If you are flying in coach, I don't know that there would be a lot of difference between AA, UA and DL. If you are flying business, I'd give it to DL if for no other reason than the DL FAs are def more hospitable, especially when compared to AA.