The best reasons are:
No physical currency involve!
There is Many reason why bitcoin is the best future currency :
1.Bitcoin is easy to understand for everyone.
2.Bitcoin price is increasing rapidly so many investor believed in bitcoin and investing more on bitcoin.
3.Bitcoin giving us many ways to earn money and make our life better.
so maybe in the future we can have this money in whole wide world and it is not impossible because people may not find it difficult to adopt it especially in this industry of social medias / web.