Writer's Block: Whose part would you play?

[the_space_cadet]

Any Doctor Who companion ever (except for Peri because while I have got the cleavage the job requires, I just couldn't stand to be that anoying).  Top of the list would be Zoe Heriot.

If they ever bring back the Rani in the new series, I think I'd like to play her.  Being a mad scientist would be fun, and of course I'd get to spar with the Doctor.