The Best Card Wallet you can find will be the one that fits your needs perfectly. Most people will look at two main factors above all else: The color and size. You will want a color that goes well with the majority of your wardrobe, and the size can be determined by how many cards you have.
The smallest card wallets will have pockets for 6 cards and the largest ones will be able to fit a dozen or more. The range in price between the two is not that significant, so this will be a small expense.
And even though the wallet will mainly be seen only when you pull it out of your pocket to pay for a purchase, you want it to aesthetically match what you are wearing. This should not be a very difficult choice to make.