Where should I incorporate my SAAS startup?

I'm British, float between Portugal and Brazil. See my paying customers as being US, Canada, AUS, NZ and UK. Want the simplest structure, banking, accounts obligations and tax. Initially I don't need to draw revenue, my plan is to grow subscriptions, I expect to get attention, and down-road would entertain investment if that door opens. Initially my focus is simple old school approach of getting paying customers, and proving the business model works.