Neither. "Time field" is the Angels' name for the field of time energy that seeps from the cracks. The Doctor seems perfectly happy with this terminology, and even repeats it once. But the crack itself isn't a time field, any more than a refrigerator magnet or a planet is a magnetic field.
The Angels call the crack itself a "rupture in time". The Doctor seems happy enough with this term as well, along with a wide variety of others (like "a split in the skin of the world"), although most of the time he just calls them cracks.
As far as we are aware, the cracks are just cracks in the universe. They lead to different places and times. Some lead to planets etc, and others lead to the end of the universe where there is pure time energy. This pure time energy generates a field (much like a magnetic field) which absorbs peoples and events and erases them from history.