Ask yourself a few basic questions, and choose your equipment accordingly. What will you be filming? Will the location be noisy or quiet? How loud is the ambient (background) sound?
Having a good quality top mic can be a lifesaver if a radio mic fails, or if you have several people to film in one group.
If you choose to hide the mic, placing it between the shirt buttons or just inside the neckline works well. Tugging the cable that leads from mic to receiver can make an awful sound, so make sure you anchor the cable - a simple loop close to the mic itself will stop any tugging.
Personal mics are great for isolating speech from background noise, and are particularly good when interviewing and recording speech in a noisy environment, or when it's not possible to get close enough to use a top mic. Personal mics are omni-directional, which means they can pick up sound from all directions. They work best when very close to the source. If your subject's not moving, then you can use a clip mic which connects directly into the camera. On the move If your subject is moving, or if they are far away from the camera, use a radio mic. Make sure the transmitter and receiver are set to the same frequency. If you are filming abroad, you must make sure your radio mics work there and are legal or you may find yourself competing with the local emergency services.
If you are recording crowd scenes where there may be sudden changes in sound levels then the 'auto' setting can be useful, but only if you are not recording speech in this environment.