Most of everyone's favorite are action tours. Very little on Europe, far east or down under. These other places are site seeing type tours, not usually action, but also great. My most memorable was going back to Normandy bringing back sad memories. We don't see ancient buildings, cathedrals, ruins, etc in the US, so that makes those tours very good.
Must admit, some of my favorite are also action type. Snorkeling & kayaking in Hawaii, helicopter up to the active volcano on big island, kayaking in Alaska, helicopter onto the glacier ice in Alaska, all the tours in Galapagos Islands, so many more. And of course sting ray city as has been mentioned many times. I have a pic of myself holding a sting ray that comes up whenever I turn on my computer. unfortunately, at my advanced age most of the action tours are behind me.
OF C'er