To me, more oppressed.

Belle only had a big deal with people gossiping about her for being different. Instead Mulan was failing to fulfil the society's expectation towards her as a young woman (bring honor for family with marriage).

By far! Mulan was nearly executed, despite being the one who defeated Huns army. The ungrateful coward was celebrated as a hero while she was dishonored. Shang didn't trust her anymore( and it's absolutely unfair IMO and it makes me think that Shang doesn't deserve her love). She was honored by the Emperor who let women in military to be mistreated... What a great honor! Nobody sympathised Mulan for her willingness to save her dad.
Mulan never got what she really deserves IMO. Her story saddened me the most.

anyday...

She had a pretty happy home life but had difficult societal expectations she couldn't meet. Belle had more freedom and privilege than any of the princesses but Pocahontas. She was well educated, had a father who loved her and supported her, was never forced or really pressured into a marriage or to stop pursuing what she loved.

She had it good at home but it's still painful to not fit in and be so lonely.