PBT means paper-based test. The PBT is the original TOEFL test started back in the 1963. There are four sections: listening, structure, reading, writing.
With the popularity of computers, the PBT changed to the CBT, the computer-based test. The CBT was replaced in September, 2005 by the iBT, the internet-based test. The CBT is no longer available. That means you have two choices: the PBT or the iBT. Which is right for you?
First, check with your school, agency or institution to find out which TOEFL score they require, PBT or iBT. Most North American schools, agencies and institutions accept only iBT scores. Why? Because the iBT tests speaking proficiency (why test speaking read the article). North American schools, etc., want to know if you can speak English. Remember: The PBT does not test speaking.
Also, the iBT is arguably the more difficult test. Why? Because of the speaking component and because you must write two essays. The PBT has only one essay. Also, with the PBT you can look at the listening section answers as you listen. For the iBT listening section, however, you see the answers only after you listen. Much harder.
So what should you do? Don't take the PBT simply because you've heard it is easier. Take the iBT. Only take the PBT if the iBT is not available. And remember: check with your institution first. Don't take the PBT, then apply, and find out that Princeton only accepts the iBT. You will waste your time and your money.