All her children except Robb was either a prisoner or running for their lives somewhere. And she thought her youngest sons were killed!

Cersei had a hard life because she couldn't control Joffrey and Robert didn't love her!

Cersei loves a man she is not allowed to love, her mother died when she was young, she lost her son, she lost her father, she fears her brother and is very desperate... She definitely has a hard life. But Catelyn has a hard life too. Her childhood may have been good but she has suffered so much in her adulthood; the birth of Jon Snow, the death of her husband, always stuck in a hard place between people who want different things, the sad things that happened to her children. It's a really tough call. I really don't know.

I guess

I don't like Cersei, but she had several problems from the very beginning. Catelyn brought hers upon herself.

Catelyn had a happy marriage. Cersei had a crappy marriage. But at least Cersei had Jamie but her side all along. Catelyn's life after Ned's execution went so downhill to the point being apart of her children, some she thought were dead... She had it worse.