Manga 43661 Owari No Seraph Userrecs

Both are post apocoliptic worlds with humanity being driven to the brink of extinction by monsters. Both have a main character with unique powers due to experiments by other humans. Both have the main characters in groups organizing coup de against the central corrupt government.  

Both have post apocalyptic worlds, and the protagonist a rash, hot headed boy who wants to kill all the (titans, vampires) for revenge for family members. Of the two, attack on titan is more gruesome, hopeless and exciting. I liked it better than Owari no Seraph, which is relatively new. When I read the first chapter of it though it reminded me of attack on titan, so give it a try! It's good in a different way. Note: I only read the attack on titan manga till the part the anime stops at (I watched the anime first). 

-Both have post apocalyptic worlds -Both MCs are motivated to exterminate all of a certain creature (Titans in SnK and Vampires in OnS) and want to become strong enough to kill these creatures. -Both of the MCs lose family early on. -Both series have a special organization who specializes in killing the series' respected enemies (Scouting Legion in SnK, Moon Demon Company in OnS) -Both have a female character whose job is basically to tell the MC to chill out and not do something stupid (Mikasa in SnK, Shinao in OnS) 

both manga is themed about human being food stock by the enemy race, both are fantasy themed and both MC wants the extermination of the enemy race... if you liked a manga where anyone dies both this title are for you 

Both begin with Eren/Yuu essentially unable to enter the 'outside world', yet they yearn to. Something happens that leads both characters through very similar struggles. Eren wishes to kill all the titans/Yuu wishes to kill all the vampires. However, both take very different turns after this stage -- there are still probably more similarities that could be drawn between the two, yet they remain individual and each deserve a read. 

post-apocalyptic, Military values with dark fantasy themes. SNK is far more polished in everything this one wants to be, therefore is superior 

The main characters both have swords, a hot temper, thirst for revenge and demonic powers.  

Both have young protagonists that have lost people in the past and fight and grow stronger in order to protect the people they love. The main characters are both lively, determined, traumatized, friendly, and spunky. 

Adapting a fictional setting with dark fantasy themes, both series has a grim story relating to the characters and its premise. The main male protagonist suffers many tragic losses in their lives including friends and family. However, their will to fight and survive becomes evident as the story progresses. Along with their experience, they are able to overcome obstacles. Yet, their world is tragically detailed with an apocalyptic-like tone. Monsters exists in both series with mysterious origins and secrets are unrivaled with horrific details.