Mmm... Female.. Or Male, I'm not sure of my choice.
I like the passion Visas feels for the Male Exile, and the consequences it implies in the battle against Dth Nihilus. And Kreia's plan seems more complete with Brianna (she knows the feelings she has for the Exile, so she manages to make the Handmaiden taking her to Atris after the confrontation with the Jedi Masters).
Also, the Handmaiden, with a Female, is doomed to stay The-Lastest-Of-The-Echani-Sisters while she has the potential to become a great Jedi.
The Disciple... Mmm... He is useful as a lab, and then... ? There isn't the same story of betrayal. And his classes Soldier>Consular, that's stupid (not enough WIS to make him a good Consular).
And, to compare with Brianna if the Exile is a Male, he preserves a good job with the Republic, and more important doesn't care about becoming a Jedi because it was HIS decision not to persevere in this way.
Sion. Mm. Yes, he is really more interesting with a Female Exile. Too bad she has to kill him. Not enough development with this idea.
What else ?
I prefer play a whole hour with a Female in underwear in Peragus that with a Male XD ..
"Do you think I seek the death of all living things? There is no victory in such things.
I do not want to win our war like this, little Jedi. When I win, I wish it to be because I was right, my teachings true."
- Kreia, Jedi Master, Sith Lord