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).
True. Bitcoins and blockchain technology has a lot of growing up to do to compete with the top dogs of money remittances. I think bitcoins may be the perfect ones to transfer with once all the problems are settled like the slow transfer rate and the transaction fees.