I started Dutch oven cooking over 20 years ago. All the camp cooks were recommending the 12" as a starter, but lately I have found it a little large for most of the things I cook. A 10" seems to be a much better size to have, and step up to a 12" if you find a need. I now have two or more of every size starting with the 5" and going up to a 17" deep, and a Maca 12"x 16". all I need now is a 22" and a hole in my head.
Here is a good camp recipe for the 10" oven. Not fast but simple and good.
1 to 1 1/2 pounds ground beef
1/4 cup Catsup, or ketchup
1 small or 1/2 large head cabbage, shredded
4 or 5 medium potatoes, diced
1 1/2 cups milk
In a 10" Dutch oven, brown beef, with 12 charcoals under oven, and drain. Place beef in mixing bowl, and add the catsup. In same oven, layer 1/2 of the cabbage, 1/2 of the potato, 4 slices of Velveeta cheese, and all the meat mixture. Add remaining cabbage and potatoes. Pour milk over all. Bake for 1 to 1 1/2 hours at 350°f., with 8 charcoals on the bottom, and 13 to 14 on top.