here are my thoughts on 25k awards (with respect to the programs in which i bank miles):

aa -- domestic awards are awesome because they have the best availability and permit stopovers (in addition to open jaws). the fees aren't very nice ime, but they win hands down for complex itins. because aa miles are so valuable, i generally try to redeem on other carries first.

as -- the fact that you can redeem for 20k is great, plus they allow stopovers (only in connection cities though). unfortunately, for me at least, it's hard to resist using as flights as a means to top off my aa and nw accounts.

co/dl/nw -- i can only comment on nw because that's where i bank most of my skyteam flights. i like the lack of booking fees and the fact that you can make unlimited online changes for $25. this means i can fly from pdx to was and return from pretty much any airport in the eastern half of the us on a whim.

hp -- you can do some pretty creative stuff with the 15k awards and availability is good ime, but i have nothing special to say about hp.

ua -- no booking fees online, but availability isn't all that good. in general, i use my ua miles for asia-related stuff.

edited to add: i had intended to start a new thread with this post but replied to this one by accident. in any case, i think the issue is somewhat relevant to the topic at hand because the value of all those miles is contingent upon how we can use them. moreover, given the fact that international upgrades are a pita on most carriers now and many, if not most, of us like to fly internationally on rev tickets, domestic awards really are one of the best possible uses of miles.