It’s a simple question really:
What is your favorite comic book series EVER?
For me, I’d have to say it would be Green Lantern: New Guardians from the New 52. This was the series that first introduced me to the Green Lantern mythos. After reading the first volume from a local library, I instantly fell in love with the characters and the idea of an infinitely powerful weapon that is only limited by the size of your imagination. It’s just super cool to me.
So how about you guys?
I would have to say Justice League (International/America) by Giffen and DeMatteis.
It was the first series that I religiously bought each and every month for five years straight.
When Breakdowns ended and Jurgens came on it lost its spark, but I held on until Zero Hour.
Then I finally said my goodbyes and looked for something to replace it, which ended up being Madman Comics.
That’s pretty cool! I’ll have to look into their run on Justice League, It seems interesting!
Agh! Just one? Don’t make me choose between Nightwing and Birds of Prey!
In fact, I’m going to be cheap and just say Detective Comics, in general.
In all seriousness, I love me some '90s/early-'00s Bat-Books. They seemed to strike a good balance between the usual Batman-ish darkness and actually being fun to read. If I have to pick something, I’ll reluctantly go with Chuck Dixon’s Nightwing run. Dick gets to be a cool dude just doing his own Nightwing thing independent of both Batman and the Titans. Great supporting cast, cool lesser-known villains, a bit of drama, a bit of action, and a sense of humor. The art’s not ideal, though. Scott McDaniel’s art makes it impossible to tell what’s going on, and when Greg Land takes over, it’s frustrating because the guy could actually draw pretty well, so it’s annoying seeing his early work (like this series) and knowing he eventually resorted to incessant tracing. That said, unless the art is really good I tend to pay more attention to the writing, so it didn’t really detract from the book for me personally. It’s just something to know going into it.
Detective Comics in general. But Tom King’s current run on Batman is great.
So difficult, but I was a HUGE fan of Superboy and the Legion of Superheroes
It’s a tie between Injustice: Gods Among Us and the New 52 Batman
I know this is a DC app, but the first one hundred issues of Lee and Kirby’s Fantastic Four is my all-time favorite comic book series. It literally is the birth and maturation of the Marvel Universe. But fear not DC fanatics, The Legion of Super-Heroes (Silver and Bronze Age) is a VERY close second.
Superman: Exile always holds a special place in my heart. If you’ve never read it, think of Planet Hulk but on a greater scale.
Watchmen, Alan Moore’s Swamp Thing, Planetary - tough to pick a winner!
@horrory Are you sure it’s not Watchmen, Alan Moore’s Swamp Thing, Planetary? 
Crisis on infinite earths
Kingdom Come
If I have to pick just one, then it’s Neil Gaiman’s Sandman.
I also find the JLI (under all it’s different names) my favorite series. Mostly due to Giffen’s run although I thought while different from what it had been to that point, Jurgens run was decent especially when Superman was leading the team. And they at least got the honor of being the Justice League to be featured in the Death of Superman story and the first to fight (and have their butts handed to them admittedly) Doomsday.
After Jurgens left the book went down hill and sadly became almost unreadable by the end, but I hung in to the bitter end anyway.
Hellblazer from Vertigo
Holy cow that’s a tough one! For DC, Mr. Miracle by Tom King. So many touchy topics were handled with tact and good taste. I’m someone who doesn’t care for excessive vulgarity, but at no point did anything in this book feel excessive. It felt real. The characters felt real. When the characters were happy I was smiling, when they were sad I was sad. The book is gorgeous and filled with nuance.
It’s one of those books I could gush about indefinitely