I am not sure about the new series, but Romana Mk 2, for the classics.
I can't help but love everything about him: his devotion to Amy, his bravery, his ability to stand up to the Doctor and give him a piece of his mind, his quirks and adorkable personality.
I want a Rory.
I'm terrible in picking favorites. I love every companion because they are all so different.
I was very devoted to Rose, because she's extremely likeable to me. I didn't liked how she treated Micky though, but alright. She will always have a special place in my heart.
It took some time for me to warm up to Martha, because the writers didn't seem to give her much personality in the earlier episodes. It wasn't until the Master showed up that I felt really connected to her, and proud of what she achieved. I did felt symphathy for her and I always feel like I can relate to her, because we're the same age, both curious and really feel the need to do something, both students and both in love with Ten (although she was slightly obsessed and I wasn't, but I can't really blame her. I mean, look at him in Smith & Jones. LOOK AT HIM. NNNNNG.)
I had to get used to Donna but I liked her right away. Her awesomeness level was pretty constant in my opinion. I loved that she was warm and caring and at the same time bossy and shouting a lot. I believe she understood the doctor better than Martha or Rose did, because she was a bit older and had more experience in life.
I have only seen two episodes with Amy thus far so I can't say anything about that.
As far as the male companions go - Jack always makes me excited and happy. Micky... I don't know. I never felt a real connection to him. I do sympathise with him but... I don't know.
I completely love Rose, she took the doctor and made him in his own words better, she is just simply fantastic, she is and always will be my favorite female companion. For the longest time my favorite male companion was Captain Jack, and then this season Rory was just so amazing, he destroyed an entire Ciber fleet dressed as a centurion to save his wife and baby daughter. How could you not love that?
once upon a time i was in love with rose tyler however I think I'm torn between Amy and Donna. Amy is just ball of energy and she's just so vivid and alive and I think that's what the Doctor needs now but Donna was literally everything the 10th Doctor needed. She kept him going and she was caring and kind. The redheads are clearly what the Doctor needs in his life :)
Amy Pond. She's spunky.
Donna is probably my favorite, by far, because she was never attracted to the Doctor like Rose, Martha, or even Amy (though her attraction was based merely on her fears of getting married) and she was always willing to take a stand against the Doctor. While a lot of companions follow wordlessly with the Doctor's actions, Donna really grounded him and proved to him that there's more to it than taking the whole universe on by himself. However, even through all of her thick-headed aggressiveness, she loved him unconditionally. She was his best friend, and that bond was something he could never replace.
Beyond Donna, I have a special place in my heart for her spunky grandad. Wilfred Mott could have been a really stunning companion had he more time with the Doctor, I really do believe. Maybe it's just because he reminds me of my own grandfather and I love how kind, lovable, and compassionate he is as a person. It's Christmas, Wilf. And it always will be with you.
Also, Rory. I don't think there needs to be any defending Rory. He's got the bull-headedness of Donna and the loving compassion of Wilfred, all while still being a nerdy and rather skittish wallflower. Really, there are so many amazing companions out there.
Oh, and do I really need to SAY Sarah Jane as far as Classic Who goes? I need to watch more of the classic series myself, but Sarah Jane is just as iconic a companion as Tom Baker was a Doctor. I mean, there's a reason why she received a parallel counterpart in the latest season of The Guild.
i like rose and amy i think :)
I used to LOVE Rose, and then Miss Amelia Pond came along and stole the title of Favorite Companion. She's bad a** but she's human, and kind, and loving, and (usually) not cold blooded.
Rory Williams is by far my favorite. i just love him
I really liked the original, Susan. I've only seen a few of her episodes (the ones on Netflix), and I really like her. She serves as a great contrast to Hartnell's Doctor. I also love Jack, because he's, well, Jack. Donna would also have to be a favorite, because she's smart, funny, and doesn't take any of the Doctor's crap.