That is the question.
For me, butter in recipes that require it, but otherwise, margarine.
Butter. Tastes nicer, and I use so little of it that it’s not going to majorly contribute to my cardiovascular risk factors.Trans fats are not that good for you either. I cook with olive, peanut, sesame or soy oil, so as far as I can, I try to eat the right kinds of fat.
Butter in recipes that ask for it, Brummel and Brown spread otherwise. Made partially from yogurt, no trans fats, no cholesterol, generally lower in fats than other “improved” margarine-type spreads, and best yet, it tastes good.
Butter all the way. To me, margarine just has a synthetic taste.
Usually butter, but I use it rarely anyway so I don’t think about it much
Margarine is for people who have no taste buds.
Butter, all the way, for me. Preferably the high-butterfat stuff, like Plugra.
Butter.
Haven’t had either in the house for months. Most likely to purchase margarine next but don’t really care, after all in either case it’s just grease.
Butter, of course!
We use margarine at my house but we call it butter
Butter. Fakey frankenfoods like margarine are evil. Butter is evil too, but in an entirely different and wholly delicious way!
Butter, margarine isn’t real man, it isn’t even real…
Couldn’t have said it better myself!
Butter. Period.
I’m not living on welfare, I’m not in prison and this country is not at war.
I don’t see why I should eat margarine.
Only butter. Margarine falls into the same category as “lite” beer, fat-free mayo, and other faux foods I won’t eat.
Butter, because margarine has trans-fats. I understand that there are some trans-fat free margarines out now, but I bought butter on sale one day and have enough in my freezer to last me a few years.
Neither, I don’t care for either and haven’t had any in the house for years. If I needed it for baking, I guess I’d buy butter because of the transfat content of margarine.
Parkay!.. 
(sorry, couldn’t resist)
Butter. I can’t recall purchasing margarine even once since we got married (13 years).