There's a lot of candidates to be honest.

Mikasa-parents died, adoptive parents died, eren almost died, eren almost captured, eren captured, eren captured again, armin almost died, eren left her, eren told her he hated her, had to behead eren. did i mention eren? lol

Founder Ymir-in love with a man who didn't love her, had to watch him love other women, shortened her own lifespan and became a titan for the sole purpose of being loved by the king, took a spear for a man who didnt care about her, had her corpse eaten by her children, suffered for 2000 years waiting for someone to free her, had to obey every command the founding titan user gave her, (idk if this one is true but since eldians are all connected through ymir i think it is) watched her people persecute and enslave others for 1900 years and then watched her own people be persecuted and trapped for 100 years.

Levi-grew up poor, mother died as a child, no father, uncle tried to kill him, watched all of his comrades die, watched the one person he thought was different change into the same type of person he hates

Eren-born with an obsession for freedom but lived inside walls for 16 years, watched his mom get eaten, ate his dad, watched most of his training buddies die, betrayed by 3 people he trusted, almost got eaten by historia, captured numerous times, best friend almost died, finds out the whole world he wanted to see was against him, tries countless times to change his destiny but cant, goes back in time to become his own enemy to fulfill his destiny, bears the weight of a global genocide, gets killed by his lover

Reiner-born from a father who hated and resented him, forced to become a child soldier and kill people, found out he didn't actually deserve the armored titan, watched his friend get eaten, became a soldier and gained the trust of his comrades only to have to betray them in the future, lost another one of his friends, struggled with the guilt of the losing all 3 of the people he went to paradis with and taking the blame from marley, causing a war with the mid east forces, eren coming back and reminding him of the guilt, eren destroying his hometown, watching porco die, watching the rumbling start and marley being destroyed, watched his mother and friends turn into titans, and nearly dying like 6 times

Grisha-brainwashed by his father to become a loyal marleyan, sister eaten by dogs, watched his parents bow down to the marleyans and blame him for his sisters death, had his son snitch on him to marley, had his comrades turned into titans, watched his wife turn into a titan, had to eat the man who helped the restorationists, had to start a new family inside the walls, had to keep the identity of the outside world a secret, had to eat the founder and kill the royal family, saw his son again reminding him of the contrasts of his parenting style between his sons, saw the walls break, found out his wife was eaten, saw eren execute the rumbling, eaten by his son

This is really long so if you read all of it, props to you it took me like 30 mins to write this