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.