Things to think about:
You MUST have a car in the Keys... nothing is walkable except Key West, and that gets old (IMO).
I'm pretty sure you'd be driving up from Key West to Key Largo to do some of your diving, so you're going to do quite a bit of commuting either way.
The drive to and from FLL can be a real problem - this can't be overstated - so don't try to do it during rush hours. Listen to the traffic (AM 610), avoid weekend traffic - especially driving BACK on Sunday afternoon! That's just wrong lol
Others will correct me if I'm wrong, but I think the best diving is mid-Keys. I could spend days on Molassas Reef, and you should see the Spiegal Grove. This is just my very humble opinion based on two dives from the south and I welcome corrections!
Key Largo will get old if you're not diving a lot... there's not much to do but dive, boat and drink.
Last suggestion is to spend a day with us on the beach at Lauderdale by the Sea or in Hollywood if it would make your drive more convenient. Hollywood is less "family" IMO. We're not the Keys here in Broward County, but it's inexpensive and you can do nice dives and fly within a few hours (17' max). Let us know if you need pointers about where to stay or how to make sure we get a dive together for when you're here.
razor:
I was wondering if anybody can recommend Key Largo or Key West. We are looking for a family oriented dive vacation. 1/2 want fly into Key West and the other 1/2 want to fly into Lauderdale and drive to Key Largo.