You can use both, but it's not necessary. I've always used a peep and had very good accuracy. I used to shoot competitively so accuracy was first and foremost. The peep will give you this.

A kisser will not usually be quite as accurate, but can be pretty darn close.A determining factor can be how finely tuned your draw length is to your body size. Most people do not or have no idea how to optimize the bow's draw length to fit themselves properly. They usually have the draw length too long and drag a kisser button back to the corner of their mouth. This generally means that thedraw length is at least an inch too long. Using the kisser to touch between the front of the lips is much better because you don't have to contort your mouth to find the same spot all the time. Aiming is usually more solid also.

Optimizing the draw length allows foryou to develop more consistent, repeatable form and once you achieve this you may find you don't need either a kisser or a peep to get decent accuracy. A good example of this is Olympic style shooters. They shoot really well out to 90 meters (100 yards) and are not allowed to use a peep. But they have their form down to a Tee.

Kisser between the lips and nose on the string (string angle permitting) and you'll be able to drill anything.