I read somewhere that the D series was the most manufactured and best seller in MCI history it passed the MCI 9 five or 6 years ago in sales. I have one of two MCI 9's in the shop now built in 1978
I've found that the longer you drive one the smaller it gets (as long as you don't forget that it is actually 45 feet!).
Isn't that really the most impactful aspect to driving a bus with skill and confidence. It is the most difficult of all things related to the bus - getting enough seat time to be fully competent. not saying that driving much less means one is not compentant - LOL