If you'd asked *me* that question, Helix (and I know you didn't, but it's a quiet evening, so's I'm just gonna jump right in anyway) I'd probably answer that YA, since the advent of the Harry Potter books -- which, although initially marketed as MG, enjoyed a ridiculous amount of crossover success with other age groups -- books by an author so fiercely loved and followed by an entire generation of young people that she nearly single-handedly created a generation of readers hungry for MORE: more heroes and heroines they could identify with, more whimsy, more magic, more adventure, more TEXT for them to absorb, and reread, and share with their friends, and talk about and write fanfic about, and stand in line at bookstores all night waiting for the next release to drop.
That's the generation that promptly read the Percy Jackson and Bloody Jack books, and was absolutely ready for The Hunger Games, and Divergent books, and they're ready for text that's more immediate and challenging than the standard third person narrative that was so longer standard for kids and YA books -- Hell, they're reading pretty much anything they can get their hands on. Kids who hunt each other with bows and arrows. Kids who go to magic schools. Books about cancer kids, and books about kids who cut, and have sex, and use drugs, and live real lives.
They're also kids who go through metal detectors and have cops stationed in their local high schools, and do shooter drills. These aren't the Bambi, Heidi, Trixie Belden, and Hardy Boys kids.
Personally? I suspect they're more sophisticated readers than their predecessors, in some ways. And they're hungry to identify with the protagonists, and first person present provides that sort of immediacy that helps them scratch that itch.