I will admit to being somewhat concerned about US Air's hostile takeover bid of Delta, not because of the anti-trust concerns (the combined airline would be the US's largest carrier and would basically own the Boston-NYC-DC shuttle routes), but because US Air sucks. If forced to fly a legacy carrier I opt for Delta (with American a close second), for no reason other than having good luck with them. On the other end of things, I think the only airline I avoid more than US Air is Continental.

Looking at the data, they're all about the same on on-time performance (Continental beats the other two nationally and at Logan, while Delta is better than US Air at Logan but not nationally). Quick comparisons suggest that I should really avoid Northwest and United. Interestingly, two of the best airline for being on-time - Southwest and Frontier - don't fly into Logan. I suppose that says something.