I'm going to go a little more obscure.
The Vangard is a fantastic size plane that has efficiency that is hard to beat and the speed disadvantage really isn't that bad considering plus it's in production a pretty long time. Plus prop maintenance is cheap.
The Mecure although being short on range moves a good number of folks for the fuel. Plus the maintenance costs are stellar (less than a 737-200 ADV)
The Trident Super 3B is underrated as heck, it's speed and efficiency is a killer that makes it actually make more money on many routes I've found than a MD80 or 727-200ADV. And cheaper maintenance than the 727-200ADV.