Aurora sought solace in dreams and singing to manage boredom.
Jasmine used Rajah to get in a practical joke or two.
Rapunzel spent the time doing all sorts of hobbies.

When Belle gets bored, she reads her favorite book over and over, and then starts "dissing her neighbors." The above three didn't do that. So Belle doesn't know how to successfully handle boredom.

Either her or Jasmine. Aurora didn't shown any boredom and Rapunzel did a lot of activities to avoid boredom and loneliness.

we see her getting bored and running out of some activities to do (no more room to paint and having to read the same books again) before it's even midday and Gothel is gone a lot of the time. At least the others had caring parents or other people to talk to

Aurora seemed pretty content and had a lot of freedom.
Rapunzel didn't really have anyone to talk to and just one small room, but she had many activities/hobbies to keep her busy and basically taught herself new skills. I don't think she was 'content' but I think she (mostly) accepted it due to Gothel's brainwashing about the outside world.
Belle clearly didn't like her provincial life but I think she was grateful for her father and she kept her mind busy by reading pretty much 24/7. At least she could escape from her boredom by immersing herself into her books and putting herself in the shoes of the characters, even if momentarily. And she had some freedom. But she would be my 2nd choice.
Jasmine wasn't content at all, she had no freedom whatsoever, pretty much the only communication she had was with a tiger (which is cool and all, but...), and felt like her voice wasn't being heard which would be tiring. Lastly she didn't have any hobbies or activities to keep her mind busy like the others, she mostly just sat and moped, so that's why I pick her.

She actually runs away unlike Belle and the others.