Martha Jones was the first that I really felt was a true favorite. She was smart. Very smart! She was not the kind of girl who would need someone to come running to save her all the time. She could save herself just as well too.
I like Amy for similar reason that I like Martha. Amy is a strong inspirational Heroine who doesn't always need to be saved. She is also a red head and Scottish which give her a fierce personality. She is also clever. She may not have the IQ of Martha but she is definitely smart. I was unsure of her when she first came but by the end of her first season I liked her.
Honestly, who could not love Rory. He is sweet, polite, nice, and very loyal. I like him because he is not the typical macho guy hero for men. He is smart and uses his brain. A bit like the Doctor in that sense. He does not need a gun to defeat his enemies. My sisters and I all agree that Rory is Awesome.
Day 8 - Least favorite companions
I don't really have a least favorite. I feel that this is unfair, but I do have companions who I feel are not quite well just. I don't know. They just have not completely won me over.
I go back and forth with Donna. On the one had her personality annoys me, but I know part of her personality is a front to protect herself from being hurt. I also find it interesting that she was truly the Doctor's best friend because she was never really interested in him romantically. She is pretty much like his sister. She also has a soft heart. However her personality makes it very difficult to like her. That is why she falls under least favorite.
I realize what an extreme shocker it is to see Rose under the "least favorite" category. I honestly feel that her character is a bit overrated. She really is not the cleverest companion compared to the others. Not that she is stupid or dumb. I also feel she is at times a bit self centered. Like when the Doctor first regenerated. She was not worried about him. She was worried about herself. She also gave up on him really fast. While I understand how difficult it must have been. I think she was a bit mellow dramatic about it. I like Rose I just do not like her quite as much as Martha, Amy, and Rory.
PS. I am not sure River qualifies as a companion but is she was She would definitely fall under the favorite category.