If you have to connect, you may want to consider NW, as I believe you're less likely to have delays flying through DTW than ORD.

In some regards, I too think NW gets a bad rap. Certainly there are a lot of aspects of their product that just aren't quite as nice (more drab interiors, mediocre first class, etc.) but I have had few bad experiences on NW and have found them far more reliable than AA, another airline I fly frequently.

NW's elite program provides free unlimited upgrades and my feeling is that you would have more luck with upgrades on NW than UA.

On the other hand, UA's F is much better, it has economy plus, it has power ports, it has nicer clubs. But it also has Chicago.