Airline mechanic here (A&P/FCC).., The DC-9 was a great a/c. The last of them Delta is retiring is the -50 version (lead sled).
The 717 is crap and very unreliable. Sure it sips fuel but leaves passengers and crew stranded.
The wisdom of the Boeing decision gradually became apparent. Early 717 operators were delighted with the reliability and passenger appeal of the type and ordered more. The small Australian regional airline Impulse is an example. Impulse took a long term lease on five 717s in early 2000, to begin an aggressive expansion into mainline routes. To the surprise of few, the ambitious move could not be sustained in competition with the majors and Impulse sold out to Qantas in May, 2001. This left Qantas with a more-or-less unwanted handful of warmed-over DC-9s to spoil the efficiency of its fleet of large Boeing and small BAe 146 jets.http://webcache.googleusercontent.com/search?q=cache:45wEO0X1urcJ:www.flightlevel350.com/Boeing-717_aircraft_facts.html+&cd=2&hl=en&ct=clnk&gl=usWithin a few months, however, the abilities of the 717 became clear. It is roomier and faster than the BAe-146, cheaper to operate, and has achieved an outstanding dispatch reliability of 99.6%. Maintenence costs are very low: a check C inspection, for example, takes just three days and is required only once in 4500 flying hours. For comparison, the old DC-9, which was always well regarded by engineering departments for its fuss free nature, needed 21 days for a check C. The new Rolls Royce BR715 engine design is highly modular: none of the line replaceable units takes more than an hour to exchange and about a third of them can be changed in under 15 minutes. Boeing claims a better than 10% operating cost advantage over the A318.
The result has been that many 717 operators, even accidental ones like Qantas, have become converts to the type. Qantas has bought more 717s to bring their fleet up to 14, and it is the front running candidate to replace their large BAe 146 fleet as well. Other significant orders have come from Hawaiian Airlines, Midwest Express, and Pembroke Leasing.