It's important to remember that many vehicles come with both a low interest rate incentive and a cash rebate. While it's possible for the same car to have more than one offer, you can only choose one incentive or rebate per vehicle either cash back or a low interest rate but you can't have both (unless you're able to choose a combination deal which, in essence, allows you to pick both with less appealing terms than if you had picked only one offer).
As a result, you need to assess your personal financial situation to decide which current offer is best for you. If the idea of paying a low interest rate (or no interest rate) for the lifetime of your car loan is appealing, then choosing the interest rate incentive is probably the better choice. However, many people prefer the cash-in-hand rebate and in most cases, they'll take the money up front and apply that rebate towards the down payment of the car.