Probably depends on who you ask, but I'd say they are relatively of equal nutrition. How "good" they are for you depends on your WOE. This link may help you figure out the differences between the two:http://www.livestrong.com/article/457609-rice-vs-couscous/
But to sum it up - Couscous is produced (it's a tiny little pasta) from wheat. Where rice is, well, rice (you are eating a kernel harvested from a plant). So if you are gluten sensitive or have a wheat allergy, couscous is not for you.
Calorically, couscous is 176 calories per cup of cooked couscous, vs 204 calories for a cup of cooked rice. Minor but I guess couscous wins there. Couscous also has slightly less carbs and slightly more protein (according to fatsecret when comparing couscous and white rice).