The Best reaction I ever get is the omni deck. Just seeing a glass block appear in your hand when you've finished a card routine is the best. Also I get really great reactions when I do PK touches. And I always get great reactions when I perform sponge bunnies for kids. The kids enjoy it and then the adults are also flipping out. It's great.
I usually get the best reactions from Reset by Paul Harris, Out of this World by Paul Curry, and Crazy Man's Handcuffs. Mentalism also tends to play really well for me.