You can advertise in all the countries, especially when you know that SFI is over 200 countries.
For me, I place priorities on two major things when I want to advertise and I will suggest that you consider them
1. The countries that are English speaking and my nationality country
2. The places where products can be shipped to without much hassles.
I consider the first point because if I recruit people from for example France when I don't know how to speak French, I will not be able to support them to my satisfaction, though there is language translator but not everybody knows how to use it and it is time consuming, if you have to pass a message or more messages to about 50 people
I consider the second point because, there are different rules and shipping charges to different countries. So I will rather recruit from where I know the laws are in place and will be convenient for my downline to follow