I ordered the Google Wallet card as soon as it was announced. The card itself is beautiful with it's all white color and the multicolored Wallet logo in the center and black "Google Wallet" text underneath. The front of the card bears no name or card number as that information is all on the the back of the card. The Wallet app itself is easy to use and it uses the card layout that Google is currently using more and more in its OS. Once you log in with your PIN that you set up you have the options of viewing your balance, sending money, viewing transactions, seeing the Google Offers currently available, and seeing your loyalty cards. If your phone has NFC and your carrier supports mobile payments then you also will have the option to use Tap to Pay. Adding money is pretty simple once you have linked a bank account or credit/debit card. Choose what card or account you want to add money from and the amount, submit the transaction and you are done. The money usually shows up within a few seconds but I have recently heard about Google holding some transactions for a few days. After you make a purchase with your Wallet card you receive a notification within a few seconds of completing the transaction telling you where the purchase was made and the amount.
This card also carries the MasterCard logo.
I found out about the American Express Serve card when I installed the Isis mobile payment app on my T-Mobile phone. Isis allows you to use Tap to Pay but it is limited to linking only a handful of cards at the moment. They give you the option of signing up for a Serve card and the sign-up was simple and quick. Adding funds to the card is similar to the Google Wallet card. Log into the app, select add money, and choose your amount. The difference is you add money directly from the app on the Wallet card but the Amex Serve card sends you to the web to add money. There were a couple of occasions where my card was declined even though the funds were available. I also did not like that it shows my remaining balance on receipts while the others don't. The Serve card is not as widely accepted as the other two but it is backed by American Express' excellent customer service.
Overall I prefer the Google Wallet card over the others with the Isis a close second. I tend to use Google Wallet as my daily user and the Isis card for larger purchases. The Google Wallet card also gets more attention and curious looks when I hand it to the cashiers. The good thing is, you can have all three of them and use them as you choose.