So, if you are in the latter category, purchase a snorkel with an easy mechanism for removing it from the strap of the mask. The mouthpiece should be comfortable in the mouth. After all, you may be biting on this for several hours at a time. As gross as it may seem, stick the thing in your mouth prior to the purchase. The dive shop should have an antiseptic spray, or at least a sink with soap and water, to apply prior to, and after doing this.
Silicone is the way to go.
Forget the black rubber varieties. They rot from oil and the sun. They do not show contamination. However, see the comments below about the minor problems with silicone. You do not need any device to keep the water from entering the snorkel when going under water.