Depends on what you're wanting, a stock pot is good because it's (usually) huge, is great for making stock (obviously) and soups, and will let you cook large amounts of pasta or crab or the like.
Dutch ovens are nice because they let you take food from the stove top into the oven. They're good for stews or roasts among other things. Because it's thick and heavy (cast iron frequently) it holds that heat a LONG time.
They're not two things that I would compare/contrast since their purposes are different. So whichever you would use more often. If you're not familiar with the two pieces, look them up on cooking sites, even just a google search and then go look in person
