I suspect you have a desktop Mac since you ask this question.
I have to admit I use neither. I don't like trackpads much, and does therefore not use one. I don't use the Magic Mouse either, not because I don't like, I actually do, but it is so slow on my iMac 5K, even on its fastest setting, my wrist actually started hurting after 2 weeks of use.
So if you have a large resolution display, and you don't mind trackpads, that would be my suggestion. If you have smaller resolution display, either will do fine. If there is a store nearby that demos the Magic Trackpad and Magic Mouse, go give either a try in the store.