@DMPony  
I have no idea. {I should mention that I despise Rose Tyler.}
 
Derpy was probably chosen because she had similar traits to ‘ugh’ Rose Tyler. {Blond, quirky, had a small time job} So that’s why she became popular.
 
Twilight would make an excellent companion to the Doctor, since she would be able to take care of herself and keep up with him in his science jargon. {Honestly, she’s kind of be like Martha….I should mention, I loved Martha.}
 
Never seen anyone do him with Colgate before. {I always headcanoned that she was his granddaughter, you know, Susan, as a pony….We can have our own ideas.}
 
Lyra is because….I don’t know. Possibly because, in some stories, he was once humanoid or something.
 
Most likely Rose didn’t become his companion was because she wasn’t that popular at the time and the other companions stuck.

For a second I thought he was holding a pregnancy test, lol.

I was always a bit surprised that Rose wasn’t his default companion. Derpy, Twilight, Colgate, even Lyra seemed more common.

Nice!

The Doctor and Rose, as it should be