Join Date: May 1998
Location: Reno, NV (RNO)
Programs: AA LT Platinum, AS, UA Premier Silver, DL, HHonors Gold, Marriott LT Titanium, Hyatt, IHG Platinum
Posts: 4,723
I agree AA is probably #1. I would rank US #2. In addition to being able to redeem miles on both US and UA, US is one of the few (the only?) major to still offer domestic coach awards at 20K (Sept 15 - Feb 29). Although award availability is not as good as AA, it has improved.
CO miles are least valuable, at least when attempting to redeem on CO. Since you can also redeem CO miles on DL and NW, they are not totally worthless.