Well I'm guessing you didn't watch Doctor Who, so even when I answer these, you might have to talk about the episodes, so in the mean time I suggest watching some.
1) The most popular doctor is the 10th, so just got with him.
2) Even though they aren't very dangerous, they're persistent and they do have constant power, so I'd say the Daleks.
3) Rose Tyler was the 9th and 10th doctors companion, and she was well loved.