The question needs to be more specific. For indoor use on the stove top or oven a dutch oven with flat bottom and roundy top is the choice. For outdoor use, as mentioned previously, the same D.O. can be used on a grill, but the preferred is one with little legs and a lidded top. The size is also of great importance. One might think they need to get the largest they can find and afford, but you need to consider what you will use it for. If you want to put a chicken in it you will need at least a 4 quart.If you want to use it for a rack of ribs then shape is another consideration, for which you will need a rectangular D.O. These are a little bit more difficult to find on the market.
The great thing about the outdoor, or legged D.O.'s is that you can stack them. We (two people) use the 1 quart size when camping and stack them with say potatoes in one and meat in the other. Sometimes you can find a D.O. at a garage sale for cheap because the lid is missing. I have one of those that I use on the grill and put it under the meat with either wood or water for smoking or steam. Other times I fill it up with coals and potatoes. Each charcoal briquet has so many btu's and you can quite accurately determine temp by the number or coals you use.
The Lodge brand is excellent and is pre-seasoned, but I prefer to buy unseasoned and do it myself. Unseasoned brands however are generally poorer quality and the castings don't always have a great lid to pot fit. You want a good fit there for the pressure effect. Beware of D.O.'s from China as they use lead and scrap metal in the casting.
I do the original seasoning with lard and thereafter with beeswax. First time seasoning turn the oven upside down so the excess drips into the fire as to prevent a buildup of gooey residue. Before using as it is heating up I use spray oil. Never use soap, only hot water and a rag, or salt if you need abrasive. If it loses its' slick, heat it up and swab it with beeswax and wipe it clean.
I have a couple of D.O.'s that have been in the family for close to 100 years and use them regularly. For great baby back ribs, throw them in the D.O. for an hour before you put them on the grill. As Jack mentioned in a recent show (#367) a D.O. is perfect for a solar oven. For this a stove-top D.O. works great. In fact I think you could almost cook in a D.O. by just sitting it the sun! I know I can't hardly pick up the lid it gets so hot if left in the sun.
For stove-top D.O.'s Gander Mountain sells one that has a lid that also can be used as a frying pan. I think that is a Lodge brand. A D.O., due to it's heavy lid, can almost replace a pressure cooker and is more practical for such things as beans, rice, etc. due to the fact that the lid can be easily removed to check on the food and to add to it without the complexity of a pressure cooker. And it is also said that the iron of the D.O. contributes to the flavor.
