> is it more useful to me to contribute to open-source software to add to my portfolio or to find people who will hire me?
Vastly more beneficial to you to contribute to OSS in my view. Nobody will really care how old you are (they'll only know if you tell them, or make it obvious in your profile) - you'll be judged only on your contribution.
The experience, both for yourself and your CV, will be worth far more than some menial task set by whoever hires you. Bear in mind that anybody who does, short of some sort of family/friend connection, either can't get or can't afford an undergraduate intern.
Vastly more beneficial to you to contribute to OSS in my view. Nobody will really care how old you are (they'll only know if you tell them, or make it obvious in your profile) - you'll be judged only on your contribution.
The experience, both for yourself and your CV, will be worth far more than some menial task set by whoever hires you. Bear in mind that anybody who does, short of some sort of family/friend connection, either can't get or can't afford an undergraduate intern.