Quote from sarah-eats-cupcakes
the best seinen is, without a doubt, Eden: It's an endless world!
...it has everything i ever wished for in a story; politics, concrete science, realistic relationships and interactions between characters, characters weren't either "black" or "white", amazing psychology and insight into the characters' personalities and finally, the mangaka obviously did tons of research, all references to different religions and cultures were 100% accurate
so yeah, eden is my number one seinen...there are many other good seinen manga ive read but listing them in order of preference will be really hard
at the time i wrote this i completely forgot about oyasumi punpun and not simple......those three are the BEST seinen i have ever read