Someone may have already given you a bit more detail about sea life but I really really enjoyed my three days at Lauderdale by the Sea when I was in FLL a couple years back. I saw octopus, turtles, tons of skates, a bunch of colorful fish, a few rays, lobster, and a bunch of other stuff, too. All in 3, 20(ish) foot night dives with an easy shore entry and no boat fees. FLL has a lot to offer, in my opinion, and it's cheap with more options for night life and eats than the Keys offer.
I can't speak for the diving in the Keys because the one time I was there I got blown out and ended up moving up the coast to Jupiter instead. We did eat well and enjoyed the diving museum in Islamorada though.
My brother and I are in the planning stages for our next FL trip and FLL is on the itinerary, as are the Keys, Blue Heron Bridge (not to be missed) and Jupiter.