Thanks for the feedback so far.

On certain trips, flying CO or DL is unavoidable e.g. group trips organized by someone else, tickets bought by employer etc. Thus service options on US and AA aren't relevant, and he needs a program to gain credit for these periodic CO & DL flights.

DL also seems to be the most logistically viable option for BDA-MEM. The CO connections in EWR dont seem to work for this city pair, resulting in a EWR overnight.

Anyone have any experience redeeming CO awards on DL metal, NW rewards on CO metal, etc.? I am curious if theres a difference between the programs from that standpoint.