Totally depends what juice you are talking about.
Freshly juiced carrots, celery, fruits, vegetables are great for you, as far as I know.
Pre-packaged juices are usually shit, and yes, some juices are just full of sugar.
Drink water and get used to it.
Since starting training seriously 8 months ago, all I drink is milk and water.
Tea and coffee once in a while.
The best part is that I have no craving for soft drinks any more at all, used to drink a fair bit. Probably averege about 1 cans worth of softdrink about once every month or so now.