I think CO has the better overall current product, when compared to AA 767-J. In terms of seat comfort, CO offers much wider seats (2-1-2 configuration vs. AA's 2-2-2), and electronic controls. AA offers a few extra inches of legroom and probably a slightly deeper recline, but the seats are just NARROW and the cabin feels crowded. CO gets the slight edge on meal service too, IMO, particularly on the Italy flights with the pasta course (unless AA offers this too, I don't know) and the separate cheese course. CO also offers more overhead bin space, with the 777-style interiors. Only a few of AA's planes offer this; the old ones have very small bins.
In-flight entertainment is a bit of a wash. AA gives personal DVD players and Bose headsets, but they're a bit clumsy and you can't watch the DVD and charge a laptop at the same time. The movie selection is sometimes cr@p. CO also offers cr@p most of the time, no NC headphones, and the videos are on a loop, so no pause/FF/Rew. BUT -- CO has the Airshow flight map. AA only has it in those few newer planes with the bigger overhead bins, which also have LCD monitors.
Now, here's the twist: by May 2007 there's a pretty decent likelihood of getting AA's new lie-flat business class seat. Based on early reports, I think that will tip the scales well enough in favor of AA, but there's no sure way to know at this point.