It depends on a number of factors, I suppose. Some things to keep in mind: if you were to have it at home, who's home would it be (yours, your sisters, another friend or relative)? How many people are you inviting? If it's not a considerable amount, it would be cheaper to have it at home then worry about the costs associated with a banquet hall. But if you're planning on inviting a lot of people (more than, say, 75) then maybe it would be wise to get a banquet room. Also, what is your sisters personality? Is she expecting something more homey, or something a little bigger? You also could look into getting a room at a local church or community center, they may be a nice in-between size, and may be cheaper.