In my experience, Delta is definitely the best of a bad lot as far as domestic airlines go. I fly them probably 95%+ of the time. When I have flown another airline (US Airways or American, now the same company) about 50% of the time there has been some BS (non-weather) delay or outright cancellation. They have hung me out to dry so many times; stranded at airports, arriving/getting back home at ridiculous hours, etc. Delta has hung me out to dry too, but nowhere near 50% of the time and when I complain they give me stuff.
I've never flown a foreign airline but hear that they blow US airlines out of the water.