I think Bitcoin is the best cryptocurrency right now,  because there are still a lot of individuals who invests in Bitcoin rather than those altcoins. Although some of the coins are catching up.
Becoming the best digital payment takes time to happen, for there has a lot of stablished digital form of payment and this is the biggest challenge for Bitcoin. Bitcoin still needs more publicity and advertise to become more popular worldwide. I think its continous fluctuating of Bitcoin value is a big hindrance to achieve such goal.