I feel jittery on all of them , but amp. Amp was one of the firsts to come out and I drank it a couple times (tastes horrible) and it never did anything. Drink you a RedBull or a Monster and I bet you'll feel something.
I can't sleep after I drink one, and the crash on them is horrible.
the 5 hour energy and the 6 hour power I cannot comment on, Ive never drank one, but people have told me its like drinking a redbull or w/e.
PS the crash on the energy drinks comes from the sugar rush and then crash following it, if you drink the sugar free ones , I have noticed that I didnt crash nearly as bad.