Amigos Del Mar also has a great pier to try out snorkeling. Hol Chan on a nice day is a great first snorkel and close to town, as well as a glass bottom boat ride with a snorkel stop would also be excellent and close. For freedom, privacy and less wave / current action I prefer Mexico Rocks, but that is farther away and will be more expensive.
Very important to me is a mask that fits, so I would recommend the first timer get a mask that fits properly(doesn't leak), or the entire experience can be awful, frustrating, and misleading.
[This message has been edited by margarita (edited 11-23-2001).]