I think XRP because earlier this day I transferred my (XRP)$20+ from one CryptoCurrency Exchange to another with a very cheap fixed fee of 0.5 XRP($0.49). I clicked all the withdrawal button of low valued coin in the exchange and guess what it requires a minimum withdrawal and it doesn't allow my $20(TRX) to be process and the fees are not fair enough in sending with only small transaction, luckily I found out that XRP is offering cheap tx's fee. So for me it is the best for small payment, maybe there are other Altcoins that offer almost free transaction fees that I'm not aware of.