Both are adaptions of Shin Megami Tensei games that revolve around demon summoning and an awesome protagonist.
Okay, so, we have all these really normal high school kids, right? What if gigantic amounts of bad shit went down, culminating in them obtaining super demon-summoning powers? Sounds silly, yes? Take it up with Atlus, that's the basic premise of both these shows. There's a good amount of mystery going on here, and the general atmosphere is pretty dark and eerie. (Although Persona 4 is most certainly the cheerier of the two.)
Both series are adaptations of a Shin Megami Tensei Game by Atlus. Also, Seiji Kishi is the director of both anime adaptation series.
Students dealing with deaths that can be predicted through some kind of mechanism. These kids can also summon beings used for fighting.
They have a very similar ambiance, feeling and are both adaptation of similar Shin Megami Tensei games. Persona 4, though, is much better.
Not only are both the series from the Shin Megami Tensei franchise but they also share that feeling of supernatural mystery. These mysteries surrounds the origins of the series as well as the characters.
In fact, the characters' cast from both series are small but contain big mysteries. Among other things, there's the usage of beasts/avatars produced by summoning of their owners. These summoned beasts fights on the behalf of their owners from both series to gain dominance; super power backgrounds.
Both series' characters also have similar age ranges and features similar artwork.
They also contain action and are directed by Seiji Kishi.
Both are anime adaptatiosn of Shin Megami Tensei games, which means they both have a similar "dark" vibe to them with a dark storyline.
A lot of demons will be the same in both games since they're part of the same franchise, for example: Pixie.
Both games ARE EXCELLENT and Persona 4 animation was good.
Kishi Seiji is the director of both anime. Adapted from famous Shin Megami Tensei JRPGs with same name.
Both anime focuses on bonds of friendship, in which can make you stronger. Demons are involved, either in a good or a bad way.
Human main antagonist are shown at the end of both anime, suggesting that humans caused the chaos in the first place.
Both anime are videogame adaptation of two of Atlus' awesome game. Persona 4's from the Persona series (obviously) while Devil Survivor sorta follows Shin Megami Tensei. And for those who are unaware, SMT follows the strict "chosen one fights demons WITH demons to save the world" formula.
This means that both series have ties to demons (or technically, mythological creatures).
P4's more concerned about bonds, while DS2 is a little darker and edgier.
Persona 4 adapted the game right, now we'll see if DS2 can do it too :D
Both have mysterious killings. Both anime have the same kind of dark ambient, and in both anime, there are a group of teenagers that fight with a kind of demons by also using demons.
Both stories are Action filled yet comedic animes with some mystery surrounding it.
Both of the anime are adapted from games, Protagonist in both stories are fighting monsters per say, by using a summoned avatar, which is Life is at stake. Both series have the same feel in terms of the story.
Both Shin Megami Tensei titles.
Both have a focus on the bonds between characters and how this fuels their powers.
Both protagonists have similar powers, in the form of summoning Personas or Demons.
Both have similar underlying themes.
Both focus on the fact that the protagonists have a limited amount of time to accomplish what they need to accomplish.
Both made by the same studio and also both based off of Shin Megami Tensei Games. You may even see some of the previous "Demons" in Devil Survivor are also "Personas" in Persona.
Same Has Summon skills to survive and if you like devil survivor 2 this will be an exact copy of it.