Main CompanionsRose Tyler
Rose is by far my favorite companion. She was the first person to travel with the Doctor (in New Who, of course) and she was the first character I connected with. She had amazing chemistry with both Nine and Ten and is the only companion besides Clara to travel with two Doctors. I don't think Clara connected with both Doctors like Rose did, though. Billie Piper's acting is fantastic (pun totally intended). She can be funny and goofy (she has a great laugh and smile), but she can also switch to seriousness in a heartbeat. (Come on, who didn't cry at the end of "Doomsday?") Also, she has a great laugh.
Rose was smart, brave, and could stand on her own, but she was also always there for the Doctor. She cared about Mickey and her family, helped others whenever she could, and always stopped to marvel at the little things in the universe. She proved that anybody can make a difference in the world. An ordinary girl can be a hero.
(Also, I ship Tenrose like FedEx. It's definitely my top OTP.)
Donna! She was in no way at any point in any way attracted to the Doctor as anything more than a friend, and their platonic relationship was refreshing. She was sassy and wasn't afraid to smack some sense into him (or anyone, really). She was hysterical and gutsy. I know some people couldn't stand her strong personality, but I thought she was wonderful. I wish she'd lasted more than a season, and I cried a lot when she left. (Why is it that the companion departures are always so tragic?)
Amy Pond/Rory Williams
I had to group these two together, because while I liked Amy on her own, I much preferred the family dynamic. It was interesting to see how three people aboard the TARDIS behaved, and I was not disappointed. While Amy was adventurous and willing to put up with the Doctor's shenanigans if it meant getting to see a new planet or alien creature, Rory was a good balance. He was able to bring some sense and logic to their travels. I think it did the Doctor a lot of good to have more people around him. It helped him to not be so lonely. Also, I'm glad Amy and Rory ended up together rather than Amy and the Doctor.
Poor Freema Agyeman had a hard act to follow. I need to go back and watch S3 again now that a few months have passed, because I think Martha deserves more credit than she gets. If she hadn't been the one to follow Rose, I think she would've gotten a lot more love. While the whole "companion-in-love-with-the-Doctor" thing was cliché (seriously, the only companion to not hit on the Doctor was Donna), Martha was definitely impressive. From the very first episode, the Doctor was calling her brilliant. Martha may be the smartest of all the companions to board the TARDIS. Not to mention she managed to keep the Doctor safe when he'd completely forgotten who he was in "Human Nature"/"The Family of Blood" and literally walked across the world for him in order to defeat the Master at the end of the season. And she was the only companion to voluntarily leave the Doctor! She put her family first, was recruited by UNIT, and ended up marrying Mickey Smith. She always helped the Doctor when he needed her, though. Everybody wins.
Ah, Clara. If so many amazing companions hadn't preceded her, I think I would've liked her more. She's definitely not unlikeable, but she's a little boring. While I like her better with Twelve than Eleven, I feel like she's overstayed her welcome. Also, I don't think the writers have any idea what they're doing with her. Her plot line is all over the place. Clara's cute and fun and great with kids, but she seems to cause the Doctor a great deal more trouble than help. She ends up getting captured or lost or trapped in near-death situations often. She frequently makes poor decisions, especially where Danny Pink is involved (such as throwing away all the TARDIS keys . . . -_-). I'm not sure how long into S9 she's going to last, but I hope we can have a new companion soon.
Other CompanionsRiver Song
Everything about River is absolutely brilliant. She and the Doctor are great together. I never get tired of their exchanges. While utterly confusing, her entire story left me astounded. I loved trying to figure out where the writers were going with her, though I failed every time. River was definitely her own person. She's the only companion I've seen break out of prison, sneak into high-security vaults, shoot bad guys, and come up with snappy retorts to everything while in a dress and high heels. And between all of this running and fighting, she somehow has time to do her makeup. She's another companion I wish we could've seen more of.
Madame Vastra, Jenny Flint, and Strax
These three are hilarious. I love Strax to pieces (especially in "The Snowmen"). Jenny is tiny, but packs a powerful punch. Vastra is very intimidating, but you can't help but like her. (And Vastra and Jenny are adorable with each other.) I hope they show up lots more in upcoming seasons.
Captain Jack Harkness
To be honest, I couldn't stand Jack for the first few episodes. The word "sleazy" always came to mind when I thought of him. (He still is, kind of.) But, after getting to see more of him, especially in "Torchwood," I can see the good qualities he has. He's funny and undeniably charming. He's the perfect part-time companion for the Doctor. (And I in no way saw the whole Face of Boe thing coming.)
It's a good thing Mickey and Martha found each other, because they get overshadowed a lot. Mickey is not a bad companion. He can be very helpful and likeable. He just happens to, unfortunately, have many other great companions to go up against. Mickey was another person I couldn't stand for a while. It was only about midway through S1 that I saw the likeable traits in him. But Mickey is definitely more than just a "tin dog."
Let's discuss: How would your companion list go? Who are your favorites/least favorites and why? And, as a bonus, how would you rank the Doctors? (My list is, from favorite to least favorite: Ten, Eleven, Nine, Twelve.)