If you want to buy a cup of coffee using cryptocurrency, doge coins and trx can be used. Because Trx and dogecoins are much cheaper and the transaction cost is less expensive and takes less time to transfer. Moreover, the use of these coins is relatively high and it is quite familiar and popular with the public. So in my opinion these two coins can be used to buy a cup of coffee.
If you take a coin based on the speed of the transaction, the cost of fees, then of course I would choose one of the coins LTC, XRP or XLM. They have some of the fastest and / or cheapest transactions at the moment. And they are the best for buying coffee.