Bitcoin isn't the strongest currency in the world, it's only the strongest digital currency in the world at this moment, cause it's holding the biggest market cap for now. Cause there are more conditions needed to become the strongest currency. I thought the biggest currency in this world for now is USD. Bitcoin needs more time to take over the marketcap. The first thing , bitcoin needs the most the it should be accepted on payment in every countries all over the world. That is the first important step which Bitcoin need to overcome. Then things will be more easier. There are already no opponent for Bitcoin in the digital currency for a long time .