It's not as simple as choosing the one card with the best redemption. You have to look at rewards in three separate ways:
1. Value of the Reward: this is how much you can get back per point or mile.
2. Earn Rate: this is how many points/miles you get per dollar spent. Many cards offer point multipliers for spending in certain categories.
3. Redemption Options: this is what you can get with your points. It could be cash back, gift cards, merchandise, direct purchase of travel, airline miles, hotel points, etc.

Choosing the best card is really a combination of all three, factoring in what you want with your rewards.