Vudu has by far the widest selection of watchable movies, but, even so, they'll be mostly movies you've probably seen before, and it'll cost you between $2 and $6 every time you want to see one. Netflix is nice because if you're going to watch movies you've seen before at least you shouldn't have to pay for it individually.
As an aside, the video content industry is so screwed up, more so in my locale because you can't get really high-speed internet without ponying up a wad to Comcast every month, which includes mandatory CATV. No matter what I do I end up owing Comcast over $120 each month. What a racket.