Both Portuguese and Spanish are beautiful Romance languages spoken by hundreds of millions of people worldwide. They have many similarities being sister languages, yet also some key differences.
Spanish is widely spoken across Latin America and Spain, making it a useful language for interacting with people in many countries. Its rules on pronunciation are also quite straightforward once you learn the basic sounds. The language has a poetic rhythm and eloquence to it that can be enjoyable to listen to and learn.
Portuguese is spoken in Portugal, Brazil, and several other countries mainly in Africa and South America. While smaller in total number of speakers than Spanish, Portuguese continues to grow particularly in Brazil which is a rising global power. I appreciate the musicality of Portuguese vowels and ability to string words together seamlessly in conversations. The language also seems somewhat easier for English speakers to pronounce than Spanish once you learn the new sounds.
Overall both languages have their merits and charm. However, if I had to choose one to specialize in, I think I would favor Portuguese slightly. The combination of its widespread use in Brazil coupled with similarities that make it easier for English speakers to learn compared to Spanish, give it a small advantage in my view. Of course, being able to learn both languages would be ideal for having access to more cultures and regions of the world. But if limited to one, my preference would be for Portuguese in the end.