I took Spanish wished I took Italian then finally did. If you are wanting to travel to Italy or go on an exchange, I would recommend Italian. It is a beautiful language and the whole Italian experience will be better if you have a basic understanding of the language. On the other hand, Spanish is more useful and practical. If you have a good teacher, it is an easy to learn language. If you live in the USA you will have more opportunities to speak it and it could help you in your career. It's great traveling in Mexico or Puerto Rico if you can speak it. Once you have learned one of these languages, it is very easy to learn the other.
Personally, I think Italian would be more fun to learn, but Spanish will be much more useful to you, especially in the working world. I can't tell you how many times I've seen "bilingual preferred" (as in Spanish-speaking) in job listings and wished I hadn't taken French instead! (Even though French is a lovely language!) My advice, take Spanish NOW while you're still in school, and you can always go back and take Italian later.