Hello msjones,
Been diving it for 17 years & still enjoy it.
The Devil's Throat, or La Garganta Del Diablo in Spanish, is a site in the Punta Sur area, with Columbia Reef to the north & Chun Chacaab to the south. It is not, however, one & the same as Punta Sur which includes other dive sites as well.
Devil's Throat is not a cave, but rather an extended swim-through. Although dark in spots & an overhead environment throughout, at all or nearly all points during the dive you will be able to see some a route of escape with ambient light, although at times this will be behind you. The most commonly used entrance is at 75'-80', and exits are at one of two main openings, one to the upper left at about 116', and another to the lower right at about 127'. It is quite a sight to exit and look out into the blue, but it is not abyssal--about 55'-65' from where you exit you can see an expanse of sand & patch reef bottom tapering downward. For much of its extent, the dive exhibits a relatively gradual slope through most of its extension & in many places has room for two divers either side-by-side or over-and-under.
For a diver qualified to do this site, an 80CF cylinder should provide adequate gas to do it, a few of the side trips, any obligated deco stops & a safety stop--I have done so. However, I prefer to do it with a 100CF or greater both because of the long string of other "throats" & swim-throughs that can be covered, and for a margin of safety. But, in many dives there I have never been seriously uncomfortable with an 80, and I'm not the world's most parsimonious on air.
As to whether it's Coz "best dive," that of course is a matter of taste. IMHO, it is very fun dive, but there are others I like better. I know a number of long-time Coz divers who share similar sentiments.
Love live Coz.
DocVikingo