From my limited experience DJ seem to swap aircraft fairly frequently so I don't get too excited until I am on board. However in "Premium" there is little difference IMHO between new and old from a practical perspective and I am happy with either. At least old has IFE.
This is not a criticism but a personal value that I have found both new and old to be fine for short haul flying. I would avoid both for anything trans-con however or international.