October Keys lobster info

If you are going as a fun vacation, with plans to lobster, fish, and enjoy some food and night-life, then I would recommend Key Largo. There are dozens of guides and outfits that will take you to reefs/holes to dive, and fish as well. Also there are numerous restaurants, shops, and bars if you are looking for that as well.
If you want a little more serious outing, then I would recommend Marathon. It seems to be more geared toward the serious lobstering/fishing enthusiast, but not the large amount of shopping/bars/restaurants. Don't get me wrong, Marathon still has all of that, just not the abundance as Largo.
If you want in-between, take a look at Islamorada.