it certainly used to be the case that you could get NW's old F seats while flying in C, because F was no longer a differentiated product.. 2 rows on the upper deck of the 747-200 was a nice ride.. (tho the one time i did that, it was still branded as F.)

i like NW's transoceanic C -- i've had some good rides there.. they've got a consistently "pretty good" product. the wines are generally respectable, the food is decent, and their cabins just don't feel as crowded to me. and DTW is a good gateway.

you can't pass up the fact that UA's seat is full flat, if you want to sleep. if you want to work or relax, i prefer the NW seat. i couldn't get comfortable for work in UA's new C -- it's a space designed for warehousing as many flat people as possible, at the cost of all else.

in paid biz with no FF considerations, i probably wouldn't pick either NW or UA. but if those are the options, i'd lean NW. i see you're ORD-based -- i wouldn't take an extra connection to get NW. (of course, i have strong FF considerations, and in reality, i'd pick UA and throw a couple of SWU's at it..)