I know this thread is for a comparison between AA and AC, but I'm beginning to feel more and more that AS is probably the most versatile program in North America and possibly the strongest for the infrequent traveler. AS allows miles to be credited from NW, DL, AA and CO (but not CO for EQM) as well as KL, AF, BA, CX and QF. Thats pretty darn strong. I believe the credit card is also available to Canadian residents.

The benefit of AC over AA is the flexibility to fly US and UA and still accumulate mileage. This is what makes the AS program so strong: when you're a price-sensitive customer, having a ton of options via AS is really going to go a long way towards shopping for price and still getting miles.