Grunge was always a favorite, both for powers and inane / outrageous personality. Burnout kind of bored me. Roxy/Freefall and Caitlin had some kickass powers and potential, but Rainmaker felt a little bit like she was sensationalist for sensationalist sake, with her 'watch me walk around naked all the time, and have I mentioned today that I'm a lesbian?'
The late lamented Gen 14 kids, particularly Ditto (duplicator) and Hardbody (teen tank with metallic skin), could also be fun to see again.
But the DV8 kids might be more suited to a grittier DCU, particularly Frostbite (absorb heat to make cold attacks, then project absorbed heat as fire attacks), Sublime (manipulates own density to be intangible or rock hard) and Devo (shapeshift into three animal/human hybrids, one bat-like, one wolf-y, one shark-ish). Perhaps Freestyle ('choose your own future lass,' able to zip through alternate timelines and choose the best result from something she's doing), as well. Their not-teen oversexed bosses / handlers (Bliss, Threshold, Ivana Baul), not so much.
Savant, despite being at least a thousand years old, always had a 'teen' feel to her (playing a little sister role to an even older Coda...).
Maxine Manchester was young, and made from equal parts killing machine and fun, fun, fun, but might not work on any super-hero team, ever, because of the killing machine bit.
Crimson / Backlash 2, the speedster daughter of Backlash, could fit, but DC already has a ton of speedsters that already operate orders of magnitude over her level.
Velocity, from Cyberforce, yet another speedster (this one a mutant cyborg) I don't think would work as well outside of her specific group/sub-continuity. (And I'm not sure if Cyberforce was even Wildstorm, come to think of it...)
Oh gosh, I just remembered that there was a terrible 'Teen Authority' too. I need to go drink something and murder the brain cell that remembered that...