What's the best program

I am looking for a program to help me construct a campaign world. Preferably something that could function on the Global, continent, regional, city, and district level. Paid is fine, though my limit is probably around $300-400. And I would only pay if it gives a distinct advantage over the various free programs out there. Online is fine, but I would prefer to have something I can work with offline. Any recommendations are welcome, but please give your opinion regarding why you think it's better than the alternatives. Thanks.

What do you want the program to do? Construct could mean a lot of different things in this context.

Are you looking for a mapping tool or a campaign management tool? For the former you could have a look at Campaign Cartographer, for the latter at Realm Works.