It's kind of a hard choice for me, but I would say Wild Thing and Steel Venom are tied for first place.
Wild Thing seems like it would be a bit like Magnum XL-200, which is definately an amazing coaster. I'm sure it has some decent airtime as well, and I really like the colour scheme.
Steel Venom, pretty much just because Impulse coasters are loads of fun, and although this one isn't as big, fast or twisty as Wicked Twister, I'm sure it's almost as good. Launches are fun as well, and this is like, the only coaster at Valleyfair that does so.