To clarify:

• Each Star Alliance carrier has their own frequent flyer program
• These programs earn miles at different rates and have different benefits
• Reward points in one program cannot be transferred to another program

Here's why I suggested you choose United over say Aeroplan:

• United tends to be the best program for earning miles when flying their milage charts are dead relatively simple with you earning 100% status milage most of the time
• United offers short-haul reward redemptions for fewer miles. Aeroplan offers a similar program but it's limited to within Canada or between Canada and the US.
• Both Air Canada and United require you to spend so much money with them to earn elite status and you're more likely to fly United being based out of the US
• If you're an elite member of Marriott you'll earn Silver Status on United.
• United does not charge a fuel surcharge on reward flights (Air Canada does and it can wipe out any savings if you aren't careful)
• The ability to earn United miles through various US credit cards
• United also offers better benefits for their frequent flyers including:
  • Complimentary extra leg room seating
  • Checked bag allowances of up to 3 bags in economy (70 lbs each)
  • Upgrades to First on most domestic routes (subject to availability)
  • The ability to change flights last minute for no charge

The other relatively good programs for earning status are Asiana and Aegean. The former will give you lifetime Gold status when you fly 500,000 miles combined on Star Alliance partners with you earning status for up to 4 years (instead of the year at a time approach of say United, Lufthansa or Air Canada). Aegean has a reduced number of miles required to re-qualify each and every year which can be a benefit if you're looking to rack up status. The problem with both programs is that unless you're flying in Flex like fares you'll have trouble racking up the miles you need for status. In addition, you won't end up using the much of the airline benefits Aegean or Asiana offer like upgrade coupons unless you fly them regularly.

Personally, I am a member of both Air Canada's program and United's. All Star Alliance travel I pay out of pocket for I'll plug my United number into since it has the higher earning rate (and for Canadians like myself there is no spend requirement) meaning most years I'll hit Gold. I use Aeroplan to collect miles from the various Canadian credit cards I have and redeem those miles for flights on Star Alliance partners (mostly United flights to avoid fuel surcharge). One nice thing about Aeroplan is that multi-city flights cost the same as roundtrips so I can fly Toronto to Dubai, Dubai to Cairo, Cairo to Zurich then Zurich to Toronto for the same miles as Toronto to Dubai roundtrip. Even when I book using Aeroplan Miles, I'll update the frequent flyer number on the award ticket to my United so I can access my United Gold benefits (i.e. lounge access, free extra leg room seating, upgrades, baggage, etc.). I also collect points towards BA (for OneWorld award redemption on airlines like American) on some of my credit cards

Obviously this strategy takes time to think up and there's no silver bullet that works for everyone. However, I can assure you it's well worth the effort when you realize the various cost savings and benefits that pour down upon you.

Safe Travels,

James