Dude. Can you say “insufficient data”? Loafers or shoes with laces … with what? A suit? Bermuda shorts? Jeans? A toga? Give me something to work with here.
In the complete absence of useful information, however, there are still a few guidelines that you may find useful. First and foremost, laces will always be more formal than slip-ons, period. You are never going to be overdressed with laces. But you could end up looking like a schmuck if you dress down with slip-ons. If you need a rule to give you an idea where the cut-off point is, try this: If you have lapels, whether on your jacket or your shirt, then go with laces. And if you have any doubts at all, leave the loafers at home. You are never overdressed with a proper shoe.
Oh – and if you are wondering, always lace-up white bucks with real Bermuda shorts. Otherwise, those shoes in the picture there? They go with damn near anything. Those shoes are hot.