I never found Ymir(freckles) to be interesting. Her backstory was believable but her decisions to live for herself by hiding her true nature was pretty dumb to me. I cant understand why she thought taking Historia along would be good, since if shes special to the church, she would most definately be raped.

I had this same issue with her; until S2 made me realize that the issue was the way Isayama told her story. We discovered Ymir's backstory bits by bits in the manga when it was necessary for the plot (Eren remembering her conversation about how she was stuck in hell for 70 years; then her entire backstory in her letter). Ymir in the manga comes across as more of a plot device instead of a character because of this; it's hard to emphatize for a character whose backstory gets revealed 40 chapters after her last appereance; her arc in CoT was the moment where we were supposed to feel for her but because we lacked context it didn't make much sense what she was doing. My reactiom to her letter in the manga was "oh, that explains her actions... ok". Doesn't help that she then gets killed off screen.

In the anime we get her backstory, we understand way more her actions and we can emphatize way more with her; S2 was her moment to shine.