I managed to break a Who panelist at Recombination last year. We were talking about relative fandoms, classic Who fans leaning towards Lit SF and new Who fans including a lot of Buffy people, and I extemporised the following theory.

Rose is Angel - the One True Love that ends in tragedy and heartache. Martha is Riley - logically a better match, but the title character isn't ready to commit. A lovestruck Donna, therefore, would be Spike.

I then had to take her to the bar and buy her a drink.