I like Silent World Dive Center in Key Largo. They have both beginner and advanced boats that go out, and they did a great job getting dives together for me at the last minute. My favorite is Looe Key, around the Ramrod Key area about mm 27 or so, north of Key West. Looe Key Dive center can do OW certs for adults and kids. The diving is fantastic, too. Lots of marine life, and usually about 25-30 ft. depths that are great for beginners.