Most people get it backwards, in my opinion. They first pick an anchor and then learn to shoot the bow using that anchor.
In my opinion, and I believe Rod Jenkins's and Rick Welch's opinions, you should learn to draw the bow to full draw and then pick an anchor wherever your hand ends up at full draw. Full draw is where your drawing forearm is in line with the arrow, viewed from above. Many people are not able to come to full draw using a finger in the corner of the mouth, so they short-draw the bow, which is not good for accuracy or getting the most out of the bow. For many people, an anchor using the thumb knuckle against the jawbone, or thumb knuckle touching the earlobe, is a better anchor because it allows them to come to full draw.