http://www.aa.com/apps/AAdvantage/Vi...artnersContent
Mileage redemption AA vs UA
US to Europe
F 125 vs UA = 100k
C 90 vs UA = 80k
US to ASIA
F 125 or 135 vs UA = 120k (the lower number is off-peak).
C 90 or 110 vs UA = 90K
UA has always been cheaper on award redemptions to many destinations.
While I do like AA's stop-over policy, most of my redemption is for international C class travel on UA.