I´m a geography and also land surveyor from Brazil.
I work for a GIS company that makes web-based map systems for cities and public orgs.
I work with open source softwares, from the database (QGIS and Postgres + Postgis) to the web map publisher (Mapserver).
Besides that, Games have always been one of my favorite hobbies. And Game Maps are incredible. I never imagined a community like this one, with so many incredible works.
What´s the best way to start these maps? With an image editor, like PS and GIMP, or with GIS softwares, like Qgis?
Opa mais um brasileiro é sempre bem-vindo!
I would advise you to look at the wonderful tutorials at the Tutorials Section, since there are many guides to create maps, textures, patterns, borders and etc in many softwares. There`s isn't a rule of thumb, since some people might prefere Photoshop (like my self), while others made some beautiful maps in GIMP, Illustrator and other softwares, also it depends on the style, you want for your map, while some softwares handle better some points then others.
Other than that, welcome again!