Wirelessly posted (BlackBerry: BlackBerry8530/5.0.0.601 Profile/MIDP-2.1 Configuration/CLDC-1.1 VendorID/417)
A lot depends on how many miles a year you fly (enough to achieve any type of elite status in either program?), and what type of benefits you hope to get from an FFP. Note that the two airlines' award-redemption schemes are very different.