I think Tiana would know what shes doing and be able to explain things well to Rapunzel as well as helping to protect her :)

I think Ariel or Jasmine would be the most eager to go, but Rapunzel's main issue is she has no idea about anything in the outside world, and neither Ariel nor Jasmine would be helpful with that. I think it would have to be Belle, Pocahontas, Mulan, or Tiana because of that. I chose Mulan because she is good at analyzing situations and adapting to them, but I could see any of those four being helpful.

But I think Belle, Mulan, or Poca, or Tia, wouldn't be willing to help Rapunzel ditch her mother. And I think Ariel might be the best at helping her sneak out.

Belle, Ariel or Jasmine.

or Ariel :)

princesslullaby agreed on that one. I can see Ariel, Pocahontas and Jasmine being helpful in terms of not condemning the fact that Rapunzel decides to run away from home because they did it before and don't see much of an issue with wanting to break free and at least try to live their lives therefore wouldn't try to preach or patronize, as a bonus they would also get a chance to go on a breathtaking adventure with Rapunzel and get to know more about the world, which is something they also want.