Elisabeth Sladen truly had chemistry, though maybe not romantic, with Tom Baker. Now Sarah Jane is etched in Doctor Who's history and she even appeared, like K-9, with David Tennant. No one is hating on the companions prior to Sarah Jane Smith but there was really something real about her that hadn't been present before. Viewers could relate with her more and she was less "cookie-cutter" than her predecessors. She even challenged the Doctor on occasions. Sarah Jane changed what it means to be a companion. Though she started out with Jon Pertwee, working with Tom Baker really brought her character out.