Ah, come on! At this point in time, this is a no-brainer. US Dollar is ruling the world in terms of popularity. The US Dollar is the most popular currency I know as of now. Every single person knows about the US Dollar. Every single person accepts the fact that US Dollar is a currency that is acceptable all over the world. Bitcoin on the other hand is a little bit unknown to many people as of now. And some others who have already heard of Bitcoin do not accept it yet.