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... 
Before you ask about a good coin for buying a cup of coffee, I think you should make sure that near your home is there is a merchant that accepted crypto as a payment method. If you know it already, the coin should be a cheap transaction fee, so all ETH and token, is not one of candidates, because we know the fee is so high. So the good coin maybe XLM, Waves, Tron