Snuba or snorkeling in Grand Turk?

[Tmaxx1]

We are going to be traveling to Grand Turk in Sept with Carnival. We are debating whether to go on a snorkeling trip with Blue Water Divers or take the snuba excursion offered through Carnival. A couple questions:

1. Can someone tell me where the Carnival excursion goes for the snuba? Do they take you to the wall? Also, when the snuba is over, do they take you back to the ship or leave you at the snuba location?

2. For those who have taken the snorkeling trip with blue water divers, how was it? It sounds like they drop you off in 25 foot deep water. Can you dive deep enough to see any thing interesting before having to go up for air? Also how long does the snorkeling last?

thanks.