So what's the best coin to buy a cup of Coffee with? Transaction cost must not be expensive and the transaction must complete before the Coffee gets cold... 
When in 2017, I know a project called PundiX "Their motto buying crypto like buying a bottle of water" Their target make a payment gateway to the whole world. I see some of their demo product, it's good and so fast, you just need to scan the QR then done. But now, I do not truly know about their development. If you interested you can go to this link https://coinmarketcap.com/currencies/pundi-x/ and learn it by yourself