Originally Posted by
Mr. S
From my experience, it's been easiest to use miles on AA and UAL.
US is as easy or easier than UA. With the exception of partners that US & UA do not have in common (e.g., TA, EI, etc.) if you can book something with UA, you can book it with US. Plus unlike UA, US does not presently block redemption on any of its *A partner airlines, so in theory US's *A redemption options are better than UA's.