The software forum a a stick post on different software.
It depends on your artistic skill. The people who make maps for Paizo have artistic ability, so keep that in mind. (If you can draw it with a pencil on paper you can do the same, or better, in gimp or photoshop or any other raster program).
If you want to use clip art or symbol libraries, then you would be best to look at a product that specializes in that (Like CC3, or FM. You can use programs like gimp to make maps with symbol libraries as well.