The main difference between the American Express Cobalt and RBC Avion Infinite Privilege cards lies in their rewards structure. The Amex Cobalt offers more varied points earning categories, including 5 points per $1 on eats & drinks, and a wide range of redemption options like merchandise and travel. The RBC Avion card focuses on travel rewards, with points redeemable for flights and a 1.0% redemption rate for non-flight travel bookings. Additionally, the RBC card provides benefits at Petro-Canada, while the Amex Cobalt offers a broader range of point usage including transfers to loyalty programs.