It's pretty tough to beat the Amex Gold as a pure points generator. As James mentioned, you earn 2x points on just about everything you buy with it, which adds up really quickly. Redemption through the Amex travel service is so-so ... lots of availability and selection, but the point value for redemptions is generally average to below average. The best value for flight redemptions is to convert the Amex points to Aeroplan (1:1) or Avios (also normally 1:1, but with periodic bonus offers of 1:1.25 or 1:1.5). Avios can be spent on BA, AA, etc. for either Y or J travel. Those can be very good redemption values, especially if you're converting Amex to Avios with a 1:1.5 bonus to begin with.

I use an Amex plat. business ... same idea, lower earn rate of 1.5x but it has other benefits that represent good value, particularly with respect to travel insurance, medical coverage, lounge access etc.

I also have an RBC Avion Infinite Visa, since not everyone takes the Amex. It also has a1.5x earn rate, redemptions are excellent for availability (you can book literally anything to anywhere), and generally average for value.

I also shy away from airline-specific reward cards since I just find them too limiting.