Welcome to the group
As far as program preference, well, that is a tough nut to crack. Some here prefer GIMP and similar programs. Some of us (myself included) swear by Prfantasy's Campaign Cartographer 3 and it's suite of programs. Others like Fractal Mapper (Similar to CC3 from what I can see).
Basically, all I can suggest is look into as manyas you can, try them out if able, look at the maps on this message board, see what kind you like the look of, and what you believe you can accomplish as well, and go from there.