I wouldn't have been averse to KNB having another shot at the franchise as I thought they did fantastic work with Predators, especially on such a short schedule. But ADI certainly makes sense. I always enjoy seeing Tom Woodruff and Alec Gillis on various "making of's" on DVDs and Blu-rays (and online) talking about the creatures and suits from various different series, so it's cool that that'll hopefully be the case again whenever The Predator Blu-ray eventually makes it out (I quite liked their commentary track on AVPR, so another one of those wouldn't go amiss).
So yes, despite some questionable design decisions in the past (which, as has been pointed out, can't necessarily always be leveled at them), they have also done some great work too, so I think they're a good choice. I just hope the faces of the Predator or Predators in this one are more Wolf than Scar. ;p
And while I'm sure lots of us would love to see or have seen Legacy get the gig, I feel like they're just priced out of the running at this point (same reason I imagine Stan Winston Studios was never involved with either franchise past Aliens and Predator 2). So ADI is really the next logical choice.