ALERT!!
Do NOT assume that the vendors used by the cruise lines are vetted! This a truly a myth, perpetuated by the lines themselves. Money talks, and little else

I agree to check out cruisecritic.com, and go to their message boards, then under Scuba review the postings and responses there- at least one company used for diving by the lines has serious issues, and these frequent cruisers/divers can save you some nightmare dealings.

If you feel comfortable in vetting a company yourself, or it taking recommendations from the other posters, it is invariably cheaper to do it yourself and usually opens up more options and MUCH smaller groupings, important in diving IMO.

S