Mine is Watchmen. All 12 issues.
Not strictly just DC but I loved the DC/Dark Horse crossover - Batman vs Predator series. Purely DC, probably The Killing Joke.
Geoff Johns Hawkman.
I’m super partial to Tom King’s Batman Rebirth. I really loved the Jokes and Riddles arc.
I love almost everything from Geoff Johns. I also really like Gail Simone’s Batgirl.
I love Elseword story and most of DC/Dark Horse crossover.
The Batman Adventures, it was one of the best comic book I’ve ever read.
Currently it is King’s Mister Miracle run. It is such a heavy and fantastic story.
For nostalgia, it’s JLA 112. The first comic I remember picking when I was very young. My favorite story line is probably the Great Darkness Saga from the LSH in the 80s. Darkseid vs. the Legion is fantastic.
George Perez’s Wonder Woman run!
Published under DC’s Vertigo, it’s hard to beat The Sandman series. Super excited for the new Sandman Universe books!
Superman #149 the original Death of Superman story and DC Special #29 the origin of the Justice Society of America.
Grant Morrison batman
Not exactly DC, but I love the Wonder Woman 77 Meets the Bionic Woman mini-series. It really is perfectly done.
The Fourth World Saga.
Batman Brave and the Bold (Jim Aparo run) and Justice League of America (early to late 1970s)
The New Teen Titans Vol. 2 issue #37 Teen Titans teaming up with Batman and the outsiders!
James Robinson’s Starman