My friend has a rule when it comes to tattoos: If you like it for two years, then it's worth getting. I totally agree with it, because tattoos will be permanent. Laser removal doesn't do the most amazing job getting rid of them and they're difficult to transform into new tattoos. That being said, tattoos can look cool and be a healthy part of self-expression. Just make sure you'd be comfortable with it, even if your skin stretches or sags (inevitable!). It helps to get a discreetly placed or smaller tattoo in case you're working in a professional environment later on. Although, so many people have tattoos that it's becoming more widely acceptable.
Piercings are a more temporary statement. You can take them out, most holes close (except those earlobe things. Do they close? I don't know.). If you are ever working somewhere where they'd be frowned on, it's not a problem. I'd go with piercings.