title_body: What coffee bean and roast are appropriate with soy milk?
upvoted_answer: Though it's not primarily your question, my chief problem with soy(a) milk in coffee is with curdling as described in this question. I have noticed curdling especially in higher-acidity coffee -- e.g., especially in American-origin coffees and lighter-roasted coffees. No matter the preparation, I avoid soy milk in anything lighter than full-city roast. The resulting grainy texture is simply unacceptable! Though admittedly certain brands are less likely to split, especially if steamed, frothed, emulsified etc. as in for certain drinks like latte.
  
  Darker-roast coffees are more common ("popular") in general at mass-market chains, so I think that can also explain some of the prevalence of dark roasts for soy milk.
  
  As for taste, fat content and sugar content vary greatly for soy milk, even when discounting other additives like vanilla or other flavourings... so go for an unsweetened, un-flavoured brand. For my preference, the nuttier taste of soy milk is a good complement for Indonesian or other southeast-Asian coffees, which can be earthy, nutty, toasty, and take to darker-roasting well. Flavour guides such as this one from Serious Eats can help identify general characteristics. If you like a pairing of soy milk with some other food, look for a coffee that expresses that same characteristic!