Just check through the lists of banned countries from a dozen of popular exchanges. You will notice that most countries that don't have strict financial policies like the US and UK plus unstable Countries that have sanctions mostly from the US appear on the list.
If it's just freedom to trade, no crypto taxation policies or bans, there are so many favorable countries including 3rd world countries. If it's in terms of adoption, you might be looking at very few countries. Most of the developed countries where adoption seems good have strict financial policies and bans on cryptos.
Also, MLMs, Ponzi and pyramid schemes seem to be so rife in Nigeria and most probably need members to make and receive payments in cryptocurrecies.
If it's just freedom to trade, no crypto taxation policies or bans, there are so many favorable countries including 3rd world countries. If it's in terms of adoption, you might be looking at very few countries. Most of the developed countries where adoption seems good have strict financial policies and bans on cryptos.
Upon having a short googling I found out that the most country that commonly used cryptocurrency is Nigeria, how this will come as I heard they banned any merchants or exchanges that associated with cryptocurrencies especially Bitcoin. But why not in Switzerland? 
If I am not mistaken, Nigeria is the country with the biggest population in Africa - 210,178,123 according to wordometer. Switzerland just has 8,703,198 peopleAlso, MLMs, Ponzi and pyramid schemes seem to be so rife in Nigeria and most probably need members to make and receive payments in cryptocurrecies.