I assume you haven't made any firm travel plans yet.
Why not try Aer Lingus? (you're going to Ireland after all)
It is a OneWorld partner and you can earn miles in AA, BA,
QF and several other frequent flyer programs.
Aer Lingus flies from ORD, BOS, and JFK to Dublin, using
Airbus 330s. (2-4-2 config.) There are a lot more seats,
compared to 767s and 757s. You have a better chance of
sitting next to an empty seat. For theri A330 seating
chart, click here:
In additoin, Aer Lingus usually have lower fares than US
carriers, especially during winter months.
Last but not least: currently Air France seems to have the lowest fare between CVG and DUB... not sure why... If you don't mind connecting in Paris. With AF, you can still earn Delta miles...
Hope this helps...