Both have multiple versions of the same person from different universes, and in general a lot of odd alternate universe science fiction.
Both have villains who are trying to find a perfect world where someone who died is alive.
Both are short on explanations of what is going on until you get near the end.
Mecha anime, mixture of humor, and a bit romance
Great characters, well design and a great story
Both anime aim is to rescue the whole world.
Both series are great, and you should take your time watching them both ;P