it really depends on how you use the points. i need to travel to toronto
regularly. to me, aa is more valuable than ua. comparison
aa: 25k + 10% back + free checked bag + less loaded (most of the time the
middle seat or even the whole row section is empty)
ua: 25k + no free checked bag (the flights I can take are all operated by
air canada) + fully loaded always.
the only thing ua is good is when i take the trip to china, but that's once
in a while, compared to the more frequent route to toronto