Problem with all of these aircraft is the same. They are built from Metal. Last summer, June/July of 2008 AWST has an article stating that Airbus and Boeing do not see the composite technology improving to a point to work in a narrow body jet until the 2018 time frame. That is their new target launch date for these next gen jets.
That said, Airbus is toying with retrofitting the 320 series with the GTF.

What this means is there is no way Delta is going to purchase a very expensive asset that 1) They will get 1/2 of the min design life out of until it needs to be replaced to compete 2) Know it is going to be obsolete in less than 10 years, 3) Is a old design that is old now, but will be gone in 10 years.
DAL is playing a game. They want a ultra efficient narrow body jet. IMHO the reason they are skeptical of the C-Series is that the big boys say that the composites cannot work until 2012-2013 to start a design of a high frequency jet.
They will wait and see how the GTF works out on that design. That is the majority of where the efficiency will be coming from. If it does they will buy in. I am sure they want a Boeing or Airbus product, and as long as fuel does not go where it was, we will band aid the problem for a few more years.