I'd prefer a freshly made sandwich but not because I'd be worried about listeria risks, I just prefer it fresh! I figure if all the stuff you're putting in the sandwich are currently living in your fridge, why would all the ingredients suddenly become a risk if they are combined into a sandwich the day before you eat them? They say the rule is don't eat leftovers which are more than 24 hours old so I say if you stick to that, it should be fine. Although I've broken that rule on several occassions - whoops!