Arex, of course. Since he has three arms he could navigate with two hands and still have a spare hand to hold an extra cup of coffee for the Captain.
I think if Janeway was picking she would want someone who is brilliant, capable, and would never challenge her authority. So no McCoy 's or Ro's, I think. I think she would choose someone like Data. Wesley would also be a possibility since she plays mama bear to several of her crew already. Hoshi might be a good fit, too, due to her linguistic skills.
If I were picking, as a viewer: Kira or Ro would create great drama representing the Maquis. Quark would end up selling the ship to the B'omar or something equally crazy every week. Garek would either be killed by the Maquis day one, or he would become a deadlier version of Seska. Pulaski would probably try to have Janeway commited. Morn would sit on the bridge silently for seven seasons and then find a way to get the ship back home, offscreen during a commercial break in Endgame.
Ultimately, I think I'd go with Guinan. She has history with the Borg and Q. She's from the Delta Quadrant. She's very wise; just think of her giving advice to each of the main characters. She's been married 23 times so she could give advice to T & B. She would be fantastic interacting with Seven. She could simultaneously pop the Doc's ego while giving him advice about humanity. On top of all that she could serve enough booze to the crew that they could tolerate Neelix.
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