Hi and welcome to LQ.
The discs to download really depend on your needs. If you want something that you can use as both a live cd and an installation disc, then download one of the Mandriva One versions. The Mandriva One discs are split into GNOME or KDE, which are different desktop environments. They are also further split by language support, but for most people who speak English, the international cd should be the one to download. If you want something with a larger selection of sfotware by default, then download the Mandriva Free cd set or dvd.