If you are a die-hard fan, like I am. There is no doubt that Tom Baker was the best there is, was, and ever will be. But I will have to give David Tennant his dew. He makes it look like playing the Doctor is fun, but when it comes to his meanstreak, you better run. Now that that's set to the table, who's your favorite assistant.
Mine is Sarah Jane even if she was a screamer, and that passive damsel-in-distress.