I would say butter, because it is a little more natural. But an even better option would be virgin coconut oil. The texture is actually solid without heat. You can substitute coconut oil for butter in baking recipes as well.
I prefer margarine over butter because butter isn't good for you. I have eaten butter maybe once in my life, and I didn't like the taste at all. Now I just stick with margarine it's healthier. I like the taste of margarine because it's really light, and butter taste weird to me.
I prefer butter. Butter is just so much tastier than margarine. And it makes taste everything better. Even plain bread can be delicious with butter. I never did like the taste of margarine as it always leave an aftertaste of oil in my mouth.
Might as well call me Paula because I put real butter on everything! I mean if you change margarine around a couple of times you have plastic. So this is kind of a scary thought! Not only that I forgot and left some margarine out all day and it was still rock solid in 90 degree heat!