Air Canada Aeroplan has some serious advantages if you're aiming for *Gold, but don't fly alot of J or F. As others have mentioned it has the lowest single-year mileage threshold: 35,000 and also does not require you to fly any of those segments on Air Canada. I actually made AC *Gold in 2008 having not flown a single flight on AC but all on LH, LX, SA and UA. The standard for most Star FF programs is 50,000 miles with some sort of minimum requirement to be earned on the airline's own metal.
What *A FFPs require you to fly their own metal? There are NONE that I know of. Certainly ALL the major FFPs I'm aware of do not have this rule. I've never heard of this before. With many FFPs you will earn more miles when flying their own metal. Some booking classes may earn miles with their own FFP and not with any other airline's FFP. Some airlines offer elite status above *G which can only be attained by flying that airline's metal (such as LH's HON circle). But for simply *G, no airlines, as far as I know, require you to fly a single mile on their metal.
OZ's program requires only 40K in two years (average 20K per year), which is a much lower level than AC's 35K in one year, and doesn't require you to fly any flights on OZ metal. So I think for 99% of frequent flyers, OZ *G would be easier to reach than AC *G (not taking into account any possible differences in earning on various booking classes). If one were to fly 35K in the first year and then none (or less than 5K) in the next year, then AC would be easier. But if someone's flying dramatically dropped off or completely stopped like that in the second year, then *G status wouldn't be much value to them. *G is only valuable when you're flying *A and not of any value if you're grounded.