5. Martha Jones
Martha, much like Katarina, was completely screwed over by the show. The companion directly succeeding Rose, she should've been something completely different a smart, passionate medical student off to see the stars. Instead she seemed intentionally hampered suffering through plotlines that made no sense (another companion who has a crush on the Doctor, how droll) and endless comparisons to Rose that became downright offensive. She's one of the biggest wasted opportunities that the show has ever had. One thing that wasn't a wasted opportunity, though, was her ending. Much like many other companions, Martha largely redeemed herself in the ending. Having suffered through the end of the world and the rage-inducing stupid of Last of the Timelords, she decides to leave the Doctor and tend to her own family instead. Martha's ending fits in with her character, what little of it was established in between long stretches of not being Rose. She's always been kind and caring, and dedicated to actually helping people. I never liked her family as much as I was supposed to, but her departure to care for them makes perfect sense. They've all been traumatized beyond relief, Martha the medical student would naturally use her skills to help. What's also in character for her is her farewell to the Tenth Doctor. Martha has tolerated god knows how long of his whining devotion to Rose, often with limited patience. The only puzzle is why it took her so long to snap, to tell him that she was worth it and leave the TARDIS on a high. Martha was always painted as being at least vaguely sensible, and we can see that here. She puts her own happiness above all else, and is finally shown to be perfectly happy as a result. And this is, really, the main reason why I like Martha's departure so much. She's the only companion to actually choose to leave the Doctor in the revived series, and does so with full dignity. She's been through absolute horrors, and only come out all the stronger. She gains self-esteem and composure, and finally realizes that she doesn't need the Doctor's validation to be truly great. She chooses her own path, much like Romana before her, and is absolutely glorious on it. ...And so, as a result, I only ground my teeth a little when she reappeared multiple times.