When I map I mainly use two different programs, Photoshop from Adobe and Campaign Cartographer 3 (CC3) from Profantasy. The programs are also used for different type of maps.
When I make world maps I prefer the freedom you have in Photoshop vs CC3, that is more of a cad program with predefined symbols that you place on your map. Where CC3 really shines is when you add in the two expansions City Designer 3 and Dungeon Designer 3. They really gives you great tools and predefined styles when it comes to making cities and dungeon/interrior maps.
All maps I do however are always finished up in photoshop. In that way my CC3 maps can get a more unique look to them.