EFIS - AFA... well, that explains a lot. What you doin' slummin over on a pilot forum? =)
The 175 has a wider fuselage cross section and wider seats. The 900 is the same narrow coffin like tube that the 200 has with newer seats but the same width. They got wise thankfully, and lowered the floor on the 700/900. XJ operates the nextgen version, which means bigger windows LED lighting etc... Seat comfort, cabin layout, bins, lights etc... are all things that will help form a passengers opinion on comfort. The fact is though, the 175 is wider and taller, which aids in comfort. That is hard to dispute. Everyone has their own opinion, but more space 99.99% of the time leads to more comfort. BTW - I think Pinnacle, Comair and Mesa all fly their 900s in the same configuration XJ does.
In the end it's the $$$$ that matters to NWA. The 900 and 175 serve their respective markets and I hope they're doing well for NWA.