For cake pops
I've never noticed a real difference in chocolate cake in a box mixes from the usual major brands. At more specialty markets like Whole Foods, independent grocers or similar you'll occasionally find better quality ingredients but pay a premium on price. If you're just at a regular chain supermarket then any major brand is fine since they'll come out about the same for cake pops.
Duncan Hines for cake mixes, Betty Crocker for brownies.