I have to agree Dundjinni and CC3 (and its plugin Dungeon Designer 3) are both great programs. However, I prefer CC3.
The learning curve for CC3 is longer than the curve for Dundjinni. And if you want fully exploit CC3 for dungeons, you really want its plugin Dungeon Designer 3 as well. Once you explore options CC3 offers, you most likely want its plugins City Designer 3 and Cartographer's Annuals as well. And it's pretty packet. However, if you decide to spend the money and learn the course, you will be able to make the most beautiful maps you could ever imagine and it will be a piece of cake.
Trust me. If you buy the CC3, DD3 and CD3 and invest time to learn them, you will never regret the spent money and you will be fully satisfied.