Personally, I think the MSN/MBA combo is better -- because it gives you an advanced degree in nursing that might be helpful/required at some point for nursing administration -- and also gives you legitimate business credentials. While the MS in Healthcare Administration is a good choice for some people, it does not give you an advanced education in nursing -- and that may become a problem if you are trying to become a leader of nurses. People with advanced education in nursing may look at you and think ("Her highest nursing degree is an entry-level degree. She never got beyond the entry-level content in nursing. She is more of a hospital administrator than a nursing leader.")
Also, the MSN/MBA combo sets you up for a DNP or PhD in nursing later if you want it. Without that Master's in Nursing, you probably have to take some extra courses to get into a doctoral program in nursing -- and that's what a lot of big-time nursing administrators are getting these days.