Double BA Major in Economics and Applied Mathematics Vs BS in Applied Mathematics-Economics

whats the difference and which one should I do ?

look at the course requirements for each. They might be different and one might allow for more courses outside the concentration(s) than the other.

In general, the BS would seem to make more sense, and that’s a pretty popular concentration. However, this isn’t a decision you need make before you even start your first year - you won’t even declare your concentration until your second year. A lot of the course requirements for the two options will overlap, so just start out taking those courses and you’ll figure things out as you go. You may even end up doing something completely different - plenty of my friends did!