I usualy do not read that much but I can't stop reading most of existing Attack on Titan Fanfics on dA and other websites it's like a virus spreading in my head. I just can't stop reading that stuff.
Many of them are so freaking inspiring that it gave me thoughts of writting my own story but I suck so much by choise of words.
My most favorite of all are Yandere!Character stories. Especialy Eren x Levi or "Ereri". I may have a lot of reader x*insert-various-snk-character-here* and simply imaginating that there is just another new OC or selfmade character (not myself in that way) some of those turn out to be realy GREAT! They make the snk-universe somewhat different like a completly different story then Attack on Titan aka Shingeki no Kyojin but dispite that fact - There are a lot of awesome stories (18+ not included).
I'm currently totaly turning crazy for a Yandere!Levi x Amnesiac!Reader story, because the writer is currently taking a break but even with there only 2 Chapters - This story is thrilling and breath taking! I totaly recommend reading this, still unfinished, story. It is mature conted/18+, because of the voilence and psychoticy going on there, so I hope if you want to read that you are over 18. Have fun and greedings.