And delicious!

Overall, a vegetarian, or mostly vegetarian (which is similar to the "Mediterranean" would probably be the best bet. There are some nutrients that are difficult to get in sufficient amounts from plants alone, though there are vegans who manage to do so. Diets that are generally high in fruits and vegetables, with small/minimal amounts of meat, dairy and other animal products are typically the healthier ones.

The Paleolithic doesn't sound too bad, but I just couldn't cut out grains or potatoes. I've cut down on potato consumption a LOT recently, and I try and stick with smaller amounts of rice and whole-grains for bread, or oatmeal for breakfast, but I love them too much to give them up entirely. And that would mean no chocolate! A diet that's higher in lean-meats instead of fatty meats would be great though - just don't overdo some of the "predator" fish that have high concentrations of mercury.

Make whatever transition you choose gradual so it's easier to stick with and follow as well as easier on your body. Maybe take a multi-vitamin supplement during the transition while you figure out what you're getting enough of, what you're not, and you could adjust to particular vitamins/minerals from there.