I have flown regularly out of LEX for six years - I used to live there. Obviously, my preferred option is NW. Two factors influenced my decision.

For one thing, as long as Mesaba are around and the leases hold up, you'll be able to ride in the ARJ out of LEX to DTW. Whether you're sitting upfront or in coach, this machine is much better than all the others that service LEX. CO uses their tapeworms a.k.a Jungle Jets to service IAH and CLE, but while I prefer these to the prop machines, they're no match for the RJ in comfort, stability or feel.

US Air used to offer Gulfstream service to CLT: quite apart from US Air's network limitations, I didn't really enjoy flying in these machines. Ditto for DL's (Atlantic Southeast maybe?) ATR-72 to ATL. I guess they are switching to CRJ's which are at least a step up.

Also, NW's fares are more reasonable, more of the time and to more places, than DL's although this depends on your Sat. night plans. The downside will be connecting to DTW in winter, and experiencing the Ohio valley thunderstorms in summer.