Both interviews are VERY relaxed...especially Nova.
Nova you meet up with 2 of their professors and it's very relaxed and conversational. They maybe will ask you a question like, "Why do you want to attend Nova?" or something like that, but other than that...they'll probably just talk about golf and the weather like they did with me. I was really relaxed when I interviewed there b/c I found out the day before that I had got into UW so I was really only there b/c I'd already paid for the plane ticket and hotel 😛
UNLV is really relaxed as well. You will have two separate interviews, one with a student and one with a professor. The student interview, at least for me, was more 'here is a list of questions I have to ask you'. The professor interview is much more conversational. What's cool is that the Dean of Student Affairs meets up and has a conversation with each interviewee at the end, which gives the school a very good and personal touch.
Overall, I liked UNLV better than Nova, simply because I couldn't handle the humid climate in Florida. However, both schools are pretty impressive and I you'd get a good education at either one.
Just my two cents 🙂
Good luck!