Well, I'm an airtime kind of guy, so I'd have to say that second airtime hill. Here's someone's video of it flying over that element (if you look closely at the very beginning of the video, to the right, you can just make out "The Innoculator" spraying its contents onto the riders just before the train passes through):
It seems to dive down into the ground a lot more than you're expecting it to do, so the airtime lasts just a little bit longer than you're thinking as you enter the hill. Damn good, and a really nice way to break up the inversions.
The main thing to say about the whole ride, is the general feeling of disorientation. Even as an enthusiast, it was genuinely difficult at points to keep a track of where we actually were on the circuit, or which way was even up, or down, haha. Very well paced ride, the whole way through, the pace of it feels unrelenting apart from the lift hill in the middle of the ride. It helps with the feeling of speed, of course, that every 2 feet or so there is some kind of near miss.
I haven't been too happy with Alton Towers about the way all this has been done/managed, but this ride is a spectacular addition to the line up for sure, and definitely well worth the wait.