Mayza,
Unless money is a real big problem, I would go to as many interviews as I could. Unless you have already been accepted somewhere where you are SURE that you want to go.
For one thing it may be the only way that you can honestly compare (from a pre-admission standpoint) each school. It is kind of like 'buying' good 'first-hand' information when you actually go to the campus on your interview day and look around, talk to some of the students and faculty and get, even if briefly, a feel for the school. It will also make the choice that you have made even stronger if you choose to stay with your original choice of schools. I have had many conversations with my MS-1 colleagues who interviewed in several places who said that they made choices about which school to go to because they "didn't like this" or "really liked that" etc ..
Second, and probably most important, you are not only going there to make a positive impression on them, but the school will be making an impression on you...either positive or nagative. You may absolutely 'fall in love' with a school where you go to interview even if you think that you are already sure that you are going to attend your original 'first choice' school. This happened to many of my classmates too!
So go and interview if you can afford the time off and money spent and go with that 'gut feeling' that you get at the end of the interview day. You will wind up in the school that is right for you and you will have more choices and more to compare your final choice to when all is said and done!
Good luck and have a great new year!
bDOc03
MS-1, UHS