Talk about some crappy choices

!!!
I wish I could tell you differently, but UX at ORD is just not reliable enough for business travel right now, sadly.
I've never been on an American RJ, but I'm sure its just as uncomfortable as a UX RJ. Even though the NW DC-9s are total pieces of you-know-what, it does sound like the more pleasant experience. Also, if you make elite status, you will get comp. upgrades, but for such a short flight its no biggie.
A couple of questions? Are these day trips, or are you a consultant-type flying out Monday am, returning Thur or Fri night? And how often or for how many weeks will you be doing this flight? Because if you go with NW, will you lose your 1K status? Or will you be able to maintain status on both airlines? That is IMHO the most important factor. YMMV.
Too bad FedEx doesn't take passengers, they have TONS of flights to MEM on BIG planes.