Watchmen is pretty popular. Virtually everyone who likes batman owns a copy of The Dark Knight Returns.
The Walking Dead trade books are certainly popular, even more than before, thanks to the hit TV show.
Maus is probably the most critically renown graphic novel... DMZ just finished its run, has a strong following, and has my vote as a likely candidate for a new classic.
If you define 'popular' as well known to the masses one would have to say that Watchmen en.wikipedia.org/wiki/Watchmen written by Alan Moore with artwork by Dave Gibbons is the the most well read and most popularly known.
On this vain the 'Sin City' series written by Frank Millar is also well known through it's transformation to the big screen.
My particular taste is for Superhero Graphic novels, and within this type, those produced from the DC stable which include Batman and Superman.
The more popular of these would be Batman Year One by Frank Millar. The Dark Knight returns by Frank Millar. The Killing Joke by Alan Moore.
Arkham Asylum by Grant Morrison.
But the Graphic Novel genre runs over all topics and books such as Persepolis by Marjane Sapatri which is about a young girl growing up in Iran after the Islamic Revolution. And Alice In Sunderland by Bryan Talbot which relates to the area and local legends.
I cant really gove you an answer,but what I can give you is a way to a solution, that is you have to find the anglde that you relate to or peaks your interest. A good paper is one that people get drawn into because it reaches them ln some way.As for me WW11 to me, I think of the holocaust and the effect it had on the survivors, their families and those who stood by and did nothing until it was too late.