Over the decades The Doctor has travelled with a range of different companions, some for only few adventures while others stick around for years at a time. When the show was re-launched in 2005, it was quite natural to expect that some of these old companions may return- and they did, including Sarah Jane Smith, and Jo Grant (although Jo only returned in the Sarah Jane Adventures, not the main show).
While it is true that many companions do return in Big Finish Productions, it would be great if some more companions could return to the small screen. It offers some great storytelling opportunities as old companions have to re-meet The Doctor as they change their face. With The Doctor now being a woman, it seems a fantastic time for some old companions to re-meet The Doctor.
While almost any companion returning could provide some great character moments for both The Doctor and said companion, there are a select few who just stand out as being better suited to return to the TARDIS for an adventure or two.