Which credit card for cash back on utilities?

Quote from porkyfan : I am buying prepaid mastercards from Kroger at $500 a time. There is a $6 fee (1.25% loss). I buy them with my Amex Blue Preferred which pays back 6%. I then get 1X gas reward points which for me is 3.5% return because I get the full 35 gallons (pick up plus two 5 gallon gas cans). Net return is 8.25%. No other card/way can beat that.

8.25% of total cash back in a nice sum, without a doubt, but realistically the credit card's cashback is separate from the gas station's cash back.

After the prepaid gymnastics, you're effectively getting 4.75% cash back from your credit card. The PenFed Visa Platinum gives you 5% without need for messing with prepaid cards, giving you a 8.5% return on gas, and has no annual fee ($75 for the Amex Blue). From a purely gas-related standpoint, there's no way the Amex Blue can win.

Admittedly, you can buy prepaid cards at the supermarket to get 4.75% cash back on everything, which isn't a terrible idea, if not a bit cumbersome. The primary problem I see is that you're losing out on the various benefits that come with the Amex. Warranty extensions are pretty pointless if you're buying food at a supermarket, for instance, but it may be worthwhile for other types of items. It's a balancing act.