Many people assume that they must be able to answer every question during an interview to be considered very successful. While that is a natural reaction, it is not very realistic; particularly given that in IT some interviews can go far a field from the specifics of your technical background and history. Additionally, realize that the impression you make during the interview is dependent upon how you answer their questions, and also upon the value of your questions.

So what's better? Well, that will vary by company, position, and interviewer. However, providing well thought out answers with your rationale and reasoning, while asking intelligent and probing questions is always a recipe of success. And don’t forget that not knowing the answer is ok, but not answering the question or trying to fudge an answer isn’t.