WELL, OBVIOUSLY TENNANT!DOCTOR/SIMM!MASTER IS THE HOTTEST THING IN THE WORLD. But I also want Jess being pretty and the question of what happens when your Time Lord lover regenerates into a different gender! Augh! Conflict!

I think that, given the choice, I'd rather Simm returned as the Master. But if he couldn't and I could pick whoever would be the next Master, I'd totally go for Jess. Possibly after she had taken a few acting lessons and developed an accent more suited to smugly superior evilness.