If you could bring back a cancelled New 52 book, . . .

[MajorHoy]

. . . which one(s) would you choose? (And maybe why?)

As far as I can tell, the books from the original New 52 first wave that were cancelled and not relaunched are:
All-Star Western
Animal Man
Batman: The Dark Knight
Batwing
Birds of Prey
Blackhawks
Blue Beetle
Captain Atom
DC Universe Presents
Demon Knights
Frankenstein, Agent of S.H.A.D.E.
The Fury of Firestorm: The Nuclear Men
Grifter
Hawk and Dove
I, Vampire
Justice League International
Legion Lost
Legion of Super-Heroes
Men of War
Mister Terrific
O.M.A.C.
Resurrection Man
The Savage Hawkman
Static Shock
Stormwatch
Superboy
Voodoo

And from the 2nd through 5th waves, the books introduced and cancelled were:
Batman, Incorporated (2nd wave)
Dial H (2nd wave)
G.I. Combat (2nd)
The Green Team: Teen Trillionaires (5th)
Justice League of America (4th)
Justice League of America's Vibe (4th)
Katana (4th)
Larfleeze (5th)
The Movement (5th)
Ravagers (2nd)
Superman Unchained (5th)
Sword of Sorcery (3rd)
Talon (3rd)
Team 7 (3rd)
Threshold (4th)
Trinity of Sin: Pandora (5th)
(Trinity of Sin: ) The Phantom Stranger (3rd)

[Cipher]

The Movement by a country mile.

Though given how it ended (as in, unplanned and ahead of schedule), I'm tempted to say William and Blackman's Batwoman as well.

And there are other characters I wish would get another shot at an ongoing, even if (and maybe even preferably if) they don't represent the book's creative teams at the time they concluded: Hawk and Dove and Stormwatch topping that list.

[Dr. Jan Itor]

Dial H for sure. It had so much potential, but was always too "out there" to find a mainstream audience. Since a lot of people will go with that, I'd add Resurrection Man just because I'm such a fan of that character.

[rhymeswithparc]

Static Shock or Firestorm, with different creative teams obviously. Those two are really interesting characters visually and, given their power sets, have potential for great stories.

[Sirzechs]

Superboy with the creative team that did the final five issues, and keep it away from crossovers and keep Kon out of the Teen titans book

StormWatch - as it was in Issue #30

[Deniz Camp]

Dial H, above all.

Batman Inc if Morrison would have stayed.

Legion, if we could have a completely new creative team.

OMAC and Blackhawks I could have done with a bit more of.

[ed2962]

I thought Frankenstein was fun.

I'd bring back Mr Terrific but with a different creative team.

[OBrianTallent]

Frankenstein absolutely.

Sword of Sorcery...but just as Amethyst.

Legion of Super Heroes.

[Starchild]

I'd bring back Hawkman, Static Shock, Larfleeze, Katana, Vibe, Firestorm, Captain Atom, Mister Terrific, Batwing & I, Vampire. As a matter of fact, all of those titles that the OP listed deserve second chances. There really isn't a lot of variety right now when it comes to DC.

[Lord of Narrative]

Definitely OMAc

[FanboyStranger]

Dial H, although I wouldn't have minded some more I, Vampire and Animal Man.

[sanderling]

Blue Beetle! I really miss seeing Jaime on a regular basis. Also Stormwatch, but with an entirely revamped premise.

[Dr. Cheesesteak]

Frankenstein would be my first choice.

Animal Man, Voodoo, JLA, Birds of Prey, Stormwatch, Blue Beetle, Sword of Sorcery, and Dial H I'd also like to see return

There are other titles I liked, but felt they ended appropriately.

[Den]

OMAC...
without a doubt.

now, if we were talking a new try with a new creative team? I'd want either Blue Beetle or Static Shock

[Flash Gordon]

Dial H, for sure. Batman, INC. if Morrison stayed longer.

Captain Atom with the same team focusing on the more cosmic adventures the end of the series hinted at. Legion, with a whole new creative team and direction.

I think Blue Beetle could have had a lot more life, under a better writer's pen.