When Douglas constructed their first jet, they thougth very much about passenger comfort but less airline flexibility. This resulted in bigger passenger windows,
spaces widely apart to allow for each row to have it's
owm window at a generious pitch between the seats.
However they didn't think the airliners would later want a much narrower seat pitch in economy class. That is itself created the lesser flexibility factor than Boeing had offered right from the start. The 707 could be tailored almost exactly to an airline needs.
However I believe the DC-8s were more economical
in fuel burn but didn't have that classy feeling the 707s
From the pilot's stand of view it is really hard to pick
one against the other. Both are excellent planes and are pioneers of the jet era.
As a child I remember my 707 flights on TWa and B-Cal,
they felt mighty especially on turns and banks.
I havent ever had a DC-8 flight. I had been on a
Cathy Pacific CV-880M which was leased to Air Malta
in the late 70s but this one didnt leave a good impression on me as it was'nt in good shape and it's air conditioning wasn't working properly especially on the ground. I wonder if it had an APU at all.