Absolutely concur with the sentiments- get your classrooom and confined water (pool work) all done in Florida.
It is senseless to sit in paradise reading a course book and doing confined water exercises. Do this in Florida.
If you are talking about a "resort course" or "discover scuba", then do whatever they have a mind to, it's tossing money and time away frivolously.
If they do the real course, by doing the preliminary steps in Florida, I would encourage them to do the Open Water portion as well.
If they are laboring under the pretense that they will enjoy the course more in the Caribbean, they are way off base. They will see nothing of note during their open water dives which are most likely held on the shallow sandy bottom with no visible life nearby.
They will likely see nothing at all until their third or fourth dive after certification whereupon the will become transfixed by rocks, sand and an occasional Squirrel Fish.
Getting "certified in the Caribbean" is a waste of time and money. My vacation time is worth more than that.
I can undesratand this intention if you are from Illinois, but Florida does offer some palatable options.
If you are dead set on this, pick your resort just as you might select a hospital for a gunshot wound. Don't go to the fancy nice hospital that does a lot of cosmetic surgery- go to the place where they get the most of that kind of traffic. If you can get a legit OW class from Club Dread or Scandals, by all means. Doubt they do much real certification by comparison, though. I think you could find a much higher completed certified total student count in Nassau (Stuart Cove), Freeport (UNEXSO), or Cayman (just pick one).