Don't use the camera mic for interviews:

Many camcorders have built in microphones. These work fine for gathering background sounds, but you should not use them for an interview. That's because the camera mic is too far away, so the sound will be hollow and noisy. Plus, it's pointing straight out (rather than up or down) so it will pick up unwanted background sounds.

As a result you should use a lav (or handheld) mic for interviews. Even an inexpensive lav will work better than a camera mic for shots with people talking.