I live in India, travel frequently, and have attained middle-tier status in three FF programs (KLM, Emirates, AC). I could probably drop the Aeroplan program but I stay in it and try to fly enough on *A each year to just make Elite.

1) relatively easy to reach *A Gold faster than on, say, LH
2) Building up my miles to eventually redeem for an RTW ticket in F class
3) Lounge access

The one drawback to AC is that they don't have any real presence in the Middle East. (However, I am pleased that they have a DEL-YYZ flight...am trying it out in a week.)

If Emirates ever decides to join Star Alliance, and start flying to Canada, I'd consider dropping Aeroplan and giving most of my business to Emirates.

My 2 cents.

JS