Go with the river tubing, it is great fun with teens. I actually live here on the Island and can say that I wouldn't really recommend much else for a 14yo boy in MoBay. There is a cheezy video arcade across from Margarittaville (which is a high priced waste of time). However, if you are looking to do some water activities, go to Aquasol. It is a small, protected beach with trampolines and you can rent jet skis, kayaks, all that stuff. Or go to the MoBay Marine Park. They offer a submarine thing or you can get snorkel equipment and check things out yourselves. Walking around MoBay is not really recommended unless you are very familiar with the Higgler/scams that are common in the Caribbean. The Old craft market is actually better than the touristy one they take you to near Margarritaville. But, you will get called to and pressured to "come inside and look". If you are looking for something specific, this is the way to shop. But, having said all that, I still think that the river tubing would be the most fun for a teen boy. Enjoy your trip.