Grand Cayman is a beautiful island with other things to do besides dive. If any of you are big on hanging out at the beach, 7 Mile Beach (actually around 5 1/2, if memory serves) is an obvious draw. You can visit the Turtle Farm and hold sea turtles, and pay for a dolphin excursion and get in the water and interact with captive dolphins (note: there are threads on this forum raising grave issues about the manner in which at least some dolphins are obtained for the tourist industry; I'm not weighing in on either side of that. Such interactions can get a great experience from a family's perspective, and I'll leave it at that). I think most of the diving is charter boat diving, although some people do shore diving. From what I've read on the forum, Grand Cayman's greatest downside is that it's quite expensive (I've been twice, single day stops, when cruising, so I didn't book a hotel).
Bonaire is much cheaper to stay on (though most any Caribbean destination has to ship in food & supplies, so it's not dirt cheap). It's not densely populated, so more 'rustic.' A drive through Washington-Slagbaai to see natural scenery (quite nice), through the donkey sanctuary (pretty neat for a trip) and around the island (arid tropical; lots of thorny plants) is fun. There are wild flamingos. If you windsurf or kiteboard, they've got those things. The island is heavily geared toward divers, so most stay at a resort at or near the ocean with an onsite dive shop, rent a pickup (stick shift!), load up their gear & some 80 cf aluminum tanks in the truck, and drive along the west coast of the island hitting different shore diving sites. Bonaire is special in that the reef is very close to shore, and you can walk in and swim out maybe 50 feet, give or take, and you're at the reef. So you can dive anytime, anywhere you want, without matching your schedule to a charter boat's. There is boat diving if you want it, though. Bonaire shoreline is mostly ironshore; rough, hard, and somewhat irregular. There's not much sandy beach, although Eden Beach Resort (which has been undergoing some renovation if memory serves) maintains a modest sand beach.
Here's one of my old trip reports from Bonaire, with lots of photos, to give you some idea what a trip there is like.
In a nutshell, if you've got a bunch of money and are being accompanied by non-diving relatives or others who may want to lay on the beach, gamble at a casino, amuse kids at the turtle farm and go 'hands on' with dolphins, and you like boat diving maybe 2 1-tank dives/day in the morning and doing other things in the afternoon, you might like Grand Cayman.
If everyone going wants to get a lot of dive bottom time in, preferably at least 3, maybe 4 dives per day (Bonaire is a great place to be nitrox certified, by the way; nitrox is often a 'free upgrade' in a package deal), don't mind hitting the grocery stores and making breakfast & lunch at your room (eating out 3 meals/day can run up costs), and you're content with some of the natural scenery and rustic feel and not keen on casinos, Bonaire might be your thing.
I prefer Bonaire for diving (I've been 4 times) for what I want to do (get in over 15 dives/trip). If I wanted to bake in the sun on sand, I could put a sand box in the backyard with a lawn chair in it.
Richard.
