Cash back bonus cards are often a better overall deal for the smart shopper. There are exceptions to this depending upon your lifestyle, but for most people this is where it's at.
The most obvious alternative to compare these cash back credit cards with is a card that pays you with "points". Typically these cards send a small catalog along with your bill and remind you that you can "cash in your points towards the purchase of these exciting gifts".
The thing to keep in mind here is that these "exciting gifts" are typically drop shipped from one of the many product liquidaters who make their money by selling excess inventory or bounty from company bankruptcy auctions. The credit card company often isn't even involved in this whole gift aspect of their credit cards. They typically contract it out to these overstock companies, sometimes for a small fee, sometimes for free, since the liquidator see's the "points" it has to give away merely as a small cost for the "leads" it gets from the credit card company.
When there are marketing people involved, few things are as they seem. The only way to avoid giving away a substantial portion of your "savings" is by getting it in cold hard cash. Cash back credit cards pay you back with cold hard cash. That way you can spend it on just what you want and it isn't diluted by the low quality of the "exciting gifts" being awarded to you with a substantial "shipping and handling" fee.
Where the comparison becomes a bit more dificult is in the realm of "airline miles" or "automotive discount" cards. Here, depending upon your lifestyle, you can often reap decent pay back from your card. That is because this is a situation in which marketing is actually working to your advantage.
Here, you've often got the big companies such as American Airlines or Ford or GM vying for the opportunity to be involved in the discount program. By providing a discount to you that is greater than the potential cash back payment, they are buying a customer - and they are willing to pay dearly for that.
Once again, the clever strategy is to shop around and compare not just the form and amount of "discounts" but also the interest rates and fees for several different cards and weigh them against your own lifestyle and habits. If you routinely purchase or lease a new car every three years, but rarely find the time for that trip to the bahamas that sounds so enticing, you're better off opting for a card that better suits you and the way you will really use it.