There's not much difference in taste, flavor, cost, or ingredients between Silk and Soy Dream. Silk is slightly cheaper than Soy Dream in many stores, and Silk has the advantage of using organic sweeteners. Both brands come in quart-sized cartons in plain, vanilla, and chocolate flavors. Half-gallon sized cartons are also available. Wildwood's carton-based soymilk is also excellent, but I haven't seen it outside of the West Coast.
Cartons are clearly the industry's future.
Right now, these products cost more than double what they should cost. Consider that dairy people are able to feed a cow exclusively organic feed, not medicate her at all, and still sell her milk for less than what White Wave and Imagine charge for their products. The ingredients for soymilk are so inexpensive that they're practically free. But this pricing situation is certain to change as the soy milk market expands. If Soy Dream and Silk aren't soon priced competitively, it's likely that conventional dairies are going to step in and offer inexpensive soymilks of their own.