definitely not the strongest, transaction time is way too slow for any practical purposes. could you imagine standing in a store for 2 hours for your payment to clear?
I think if you are talking about transaction, it is not related about being strong but the efficiency of the digital currency. Bitcoin is said to be strong because it has a lot of users and supporters, even many people are earning other digital currency, they are just using it to convert it on bitcoin. So, as a digital currency bitcoin is the strongest.
Bitcoin is the strongest of the cryptocurrency because almost all the alts depend upon the bitcoin and the price increase and decrease of the bitcoin has a great impact on the price of the alts. So, this makes bitcoin the strongest currency of the crypto world.
But when talking about the worlds currency and the ranking of bitcoin in front of these currencies is still too behind, bitcoin is a progressing currency and not known in many places in the world yet.
Oh, so does that mean today, you'd rather keep in your account to hold for five years either Indian Rupees or US Dollars?? And not Bitcoin??
That in five years, your fiat will be better enabling you to afford the cost of:
-Paying one full year worth of apartment/house rent in an expensive city in your country, or
-Affording healthcare/hospital expense for someone in your family, or
-Moving to another country and paying related costs, or
-Paying for higher education at a nice school for a family member, or
-Helping start a business and pay labor costs for yourself or friend/family