There's more than one kind of sugar. Juices have both fructose and glucose; the former is more likely to be stored by the liver, the latter is deployed more widely around the body. Soda has much higher levels of fructose than glucose, thanks to all that high-fructose corn syrup that has become so popular with food manufacturers. There seems to be mounting evidence that high fructose intake is correlated with increased obesity. Here's a recent article on the topic: http://www.theguardian.com/society/the-shape-we-are-in-blog/...
If you head to YouTube and look for Dr Robert Lustig, a researcher at UCSF, there's a 1 or 2 hour lecutre he has delivered on this topic which goes into great detail ont eh different metabolic pathways different kinds of sugar take within the body.