The MD-80 and DC-9 are the trailing edge of technology. The airplane is built "hell for stout". Back when US Airways operated both the 737-200 and the DC-90-30, I heard from a heavy maintenance mechanic that when you stripped the aircraft down in a "D" check they found that the DC-9 was about 10,000 lbs heavier than the B737-200.
Bad news for that was the a additional fuel burn on the DC-9 over its lifetime. The good news was that as a high time air-frame it looked great. Our old B737's were all covered with "scabs", large skin patches covering ground damage. The DC-9's had almost none. The joke was when you drove a tug into a DC-9, you broke the tug. The DC-9 slat extension speed is 280Kt. We used a company speed of 250. first flap extension was also 250. The airplane is built like the proverbial little house.
We had many DC-9 pilots transition from the 9 directly to the Bus. One old guy said, "now I know what it's like to be a dog watching television."