I got a bucket-load of Asia Miles which I have only used on AA:
Pros:
- Often better availability than AC on Canada-US flights
- Super cheap fees ($40 YYZ-BOS v. $160 on Aeroplan)
- Allowed to put bookings on "hold"
Cons:
- Have to call-in to book (little-to-no wait once there, and the agents are very competent, and speak good English)
- Must book 3 business days in advance