Acai has way more fructose in it that a lot of other berries. Make sure you brush your teeth. Same deal with pomegranates, although you can make grenadine out of them and that shit is awesome for cocktails!
If you're after antioxidants, blueberries are the way to go. They're so red, they're blue. I know how contrary that sounds, but ask a professional dietitian. They're also high in vitamin C.
As for Acai fruit giving you energy?
I get the feeling any benefit is a mixture of psychosomatic effects and a boost in vitamins that a lot of people are lacking due to eating overly processed foods nowadays. If you're already eating 2 fruit / 5 veg a day, you probably won't notice a thing.
The pills? Now I'm pretty certain, just like any other genuine diet pill, they've got speed in them.