1. Justice League
Justice League by Geoff Johns with many great artists. 2011-2016. The flagship DC title of the New 52 plus the Forever Evil event (2013-2014). It starts with the origin of the team and it continues to one big story after the other. Justice League is one of the two consistently best titles throughout the entire New 52 era. You really shouldn't miss this one.
Batman by Scott Snyder with Greg Capullo. 2011-2016. The other one of the two consistently best titles of the New 52 era. The title starts strong, stays strong and ends strong. It's definitely the title to look for.
Aquaman by Geoff Johns with Ivan Reis and Paul Pelletier. 2011-2013. The first four volumes (or 25 issues) were one of the best comics out there month after month. After Geoff Johns left the title Jeff Parker took over for issues 26-40 and he did a fine job. Volume 5 (Sea of Storms) was a tone down from the previous volumes but volume 6 (Maelstrom) was great again. Issues 41-48 (Volume 7 Exile) by Cullen Bunn were not that good and the characterisation was way off. The final New 52 issues 49-52 by Dan Abnett who will also be the Aquaman writer in Rebirth were great again, definitely on par at least with Jeff Parker's Maelstrom. So you should get volumes 1-4, you might want to check out volumes 6 and 8, you could get volume 5 or not, and you should probably skip volume 7.
4. Green Arrow
Green Arrow by Jeff Lemire with Andrea Sorrentino. 2013-2014. Volumes 4-6 and also a Deluxe Edition (issues 17-34). Green Arrow was not good before this team and after this team, but Jeff Lemire gave a story worthy of the Deluxe Edition treatment. Great story, great character development, great antagonists, with nice art, if only this team could stay on the title a little longer.
5. The Flash
The Flash by Francis Manapul and Brian Buccellato. 2011-2013. Volumes 1-4, issues 0-25. After Flashpoint the creative team starts with a fresh, young Barry Allen as the sole speedster known as The Flash. The stories are good, they play with Barry's character, his classic villains (Grodd, the Rogues, a new Reverse-Flash) and the art is always top-notch. Their run will be collected in an omnibus at the end of the year so if you are interested make sure you get that. Then volume 5 (issues 26-29) has a small filler story which was kind of fun but you could feel that it was filler. Robert Venitti and Van Jensen with Brett Booth take over the title in 2014 with issue 30 until the end of the New 52. Volumes 6-7 (issues 30-40) are essentially one big story and it might feel like it drags a little too long but it's really fun. Volume 8 (issues 41-47) was an epic confrontation between The Flash and Professor Zoom (Eobard Thawne) and was really nice in my opinion. Then to prepare for Rebirth, Robert Venditti and Brett Booth left the title and for issues 48-52 we got a story with The Flash against the Riddler (normally a Batman's villain). I felt the quality dropped a little in this last arc. So you should probably get the omnibus (instead of volumes 1-4), you might want to check out volumes 6-8, and you might want to skip volumes 5 and 9.
6. Green Lantern
Green Lantern by Geoff Johns with many great artists. 2004-2013. Continues directly from the previous volume. Collected in three gorgeous omnibi, this is the title you don't want to miss. From "Green Lantern Rebirth" to "Sinestro Corps War" to "Blackest Night" to "Wrath of the First Lantern" buying these three omnibi will be the best money you have ever spent on comic books. Amazon has some pretty generous discounts on them so make sure you get them before they go out of print.
Green Lantern by Robert Venditti with Billy Tan. 2013-2016. Robert Venditti takes the baton from Geoff Johns which is a really difficult task but he manages to live up to it. There were some controversial changes in direction which were mandated from the editors, but Venditti makes them work, he writes an amazing Hal Jordan because he understands his character, and some of his later stories and their repercussions will be dealt with during Rebirth in Hal Jordan and the Green Lantern Corps. The art is fine though sometimes I find it lacking a little depth. Volumes 4-8 (issues 21-52), it's a nice title worth checking out.
Superman by Geoff Johns with John Romita Jr. 2014-2015. Issues 32-39 collected in "Superman The Men of Tomorrow". Superman suffered a lot during the New 52 but this is one of the few really good Superman stories and it has elements that will play out in Rebirth. The art is really unique and it's really hit or miss so keep that in mind.
8. Superman: Lois and Clark
Superman Lois and Clark by Dan Jurgens with Lee Weeks. 2015-2016. Heading into Rebirth you should know that New 52 Superman died and the Superman from before Flashpoint will take up his mantle. This mini-series deals with how the married with Lois Lane and having a kid Superman survived, lives in this universe and hides his existence from the other heroes while still helping during a crisis. Great title with a Superman that has heart and soul and great characterisation.
9. The Final Days of Superman
The Final Days of Superman by Peter J. Tomasi with many great artists. 2016. An 8 part crossover story that deals with the death of the New 52 Superman. It had really good writing, and directly leads into Rebirth. Great title and a really important story you wouldn't want to miss.
10. Batman and Robin
Batman an Robin by Peter J. Tomasi with Patrick Gleason. 2011-2015. A really strong team delivers a really solid title that deals with the dynamic between Batman and his son Damian Wayne the fourth Robin. The only slight problem is that it's not the main bat-book (Batman is) and some of the things done in Batman (or Batman Incorporated) play out in here but they still work out fine. Worth checking out.
11. The Omega Men
The Omega Men by Tom King with Barnaby Bagenda. 2015-2016. A really dark book. A really good book. Tom King is a great writer. The art fits this title very well. The book also features the fourth Green Lantern from Earth Kyle Rayner who is considered a fan favourite so this might attract you to it. It's really cheap on Amazon for 12 issues so I think it's well worth your money.
Grayson by Tom King, Tim Seeley with Mikel Janin. 2014-2016. Dick Grayson the first Robin and Nightwing infiltrates an organisation named Spyral as a spy on behalf of Batman. The book is really good, in terms of both story and art. I have two slight problems with it. First of all the creative team leaves the book with issue 17 to focus on their Rebirth projects and a new team (Jackson Lanzing and Collin Kelley with Roge Antonio) has to wrap up the series and while they aren't bad, they are not on par with the original creators. Secondly, you have to get five volumes for 20 issues and this feels a little like cheating because five volumes normally cover about 30 issues. Still it's a pretty solid series just keep what I said in mind.
13. Superman Unchained
Superman Unchained by Scott Snyder with Jim Lee. 2013-2014. A mini-series to celebrate 75 years since Superman was created. The story is quite good, the art is amazing. It was originally supposed to be 12 issues but Jim Lee is really busy so it ended up being 9 issues and you can feel it wrapping up a little fast. It is still really solid and worth checking out.
14. Justice League of America
Justice League of America by Geoff Johns, Jeff Lemire, Matt Kindt with many great artists. 2013-2014. A supporting title to the Justice League one during the Trinity War and Forever Evil storylines. Really nice concept with great art. Definitely worth checking out.
15. Martian Manhunter
Martian Manhunter by Rob Williams with Eddy Barrows and Ben Oliver. 2015-2016. A well-written, dark book, that plays with Martian Manhunter's mythology and introduces some interesting concepts with pretty solid art. Worth checking out.
16. Titans Hunt
Titans Hunt by Dan Abnett with many artists. 2015-2016. The return of the classic Nick Cordy influenced Teen Titans team. Really nice books and Dan Abnett can write some very strong script. Worth checking out and kind of important heading into Rebirth.