We have been using the free and open source Quantum GIS (QGIS) quite a bit over the last few months. The newest version of QGIS, version 3.0.0 (Girona), has been released and is available for download free of charge here:
It is amazing to see the capability of QGIS these days. If you are just getting started in the GIS world I would start by learning QGIS. If you are experienced in your GIS capabilities then give it a try.