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... 
EOS, Doge, and Tron... these three Altcoins are very comfortable to use for payments/fund transfers IMO. very cheap fees and fast transaction processing even before the 'hot coffee goes cold'.
Tron to me is my best bet before the coffee gets cold you'll get the payment, but scalability will be a big issue when many users are going to use Tron, Ethereum could be a big bet unfortunately with so many traders using Ethereum sometimes it will take from one minute to 30 minutes because of the DeFi hype.