The answer is that it often is not, at least for most people, most of the time. Eventually it will be the best payment system, but it needs to develop further, gain more adoption, and get over the scaling obstacles. Even so, Bitcoin is already the best payment system for certain use-cases, such as sending money across borders, or receiving money from someone you don't trust (which helps further in cross-border transactions).
Most people might still misunderstood what bitcoin and block chain technology is. May be once they realize how far the cryptos are from the money scams, they will be delighted to have bitcoin as payment system. I can see that as more and more industries are accepting bitcoin as payment, more people will say it is the best currency and method of buying products and services through online transactions.