In the more recent year worlds, I have really enjoyed using the Dash 8-400s. They give a decent capacity for some of the 2nd and 3rd tiered cities and return a good profit. Plus they have a nice speed and lower fuel burn compared to come of the CRJ and ERJ family with similar capacity.
For larger jets, I'm not too sure on that one. I think based on price offered and seating, the A-319 provides a really good return. I would look like to try an airline with more Boeing narrowbody's, but in AM, outside of the 717, the A-320 family are a better investment.