Hulu is great, but the only thing it has over Netflix is that it has more TV shows and the most recent season of like every popular show (for Netflix the shows are usually a season behind). Hulu does not have that many movies, especially when compared to Netflix.
I love Netflix. Granted, I've only tried free Hulu and not Hulu plus. I believe you can have atrial period of both? I suggest starting one, get to see if you like it. Then try the other. Although, since your sister already has Netflix, you can get Hulu Plus and use both!
I haven't tried hulu though a few shows I like I've seen on there. To me netflix has the widest selection. My combo that works great is I have a Amazon Prime membership that I share the benefits (video, music, book loans) with my family and in return my parents share their netflix which has me covered for 90% of my content.