AA's work like UA's except for one big difference... the AA certs can be used on ANY fare, even e-fares.

AA agents are also a lot nicer than UA agents about looking at inventory before you book a ticket to see if an upgrade is available. My usual experience with UA is that they make you take your chances and only then will look to see if they can secure you an upgrade or force you to waitlist.

In a "normal" year, they might be an almost equal trade. This year, however, their life has been extended since they haven't worked the kinks out in the electronic redemption program so the 2004's (VIP04s) are much more valuable than UA's SWUs (expiring 1/05) since they don't have the looming expiration period.