I've been a Smart user from the start so Smart for me.

*CNS: I used to pay in Smart center in malls via that machine. But when it became problematic and didn't want to accept some of the bills, I went to the bills payment section of SM and have been paying it there since. If you will pay more than your total amount due, your excess will be deducted in your next bill so you don't need to worry if the machine won't give any change.