I think you should definitely start with Spanish. It's a lot more useful and widely spoken than Portuguese. My plan now is to study other languages first (and to study Portuguese later), but earlier this year I studied a little bit of Portuguese. I realized that the Spanish I knew really helped me understand Portuguese. They're very similar. It's probably better to start with Spanish (there are also more learning resources for Spanish) and then when you're intermediate you could begin studying Portuguese. I wouldn't recommend starting both of them from scratch at the same time. Whether you start Spanish first or Portuguese first, knowing one will help you study the other one later. But Spanish is the more useful one to know.