Active Level 6
Samsung Pay is the best App I can think of in the Galaxy Store.
I use Samsung Pay for my everyday purchases. This helps me not carrying my wallet with Cash or card everywhere I go. It supports all the banks that I am using right now. 
What makes it even better is, it almost works everywhere I shop. Also, I feel secure as only I can unlock my phone using fingerprint. 
It also supports adding membership cards, which as a Canadian I feel must use feature on this application!
Now that I have Galaxy watch, I am using my watch to pay for the things.
Not only it is convenient but I feel it is the best App I have ever used!
As a software engineer, I can think of the smart work being done on this application. 
And lastly the best promotion for Samsung Phone is the Samsung Pay application. Why? Because when I go to places where Tap isn't acceptable and still I use my phone, I get same reaction. Which phone it is? Its Samsung ofcourse!