Netflix is basically movies. A few independents, a few popular ones.
Hulu is TV shows. Some of those are indie too, but they do mostly the network stuffs.
Amazon is a mixture of the two I think.
I had Netflix for a long time. Thought it was better at giving me stuff to watch. With Hulu, you're stuck waiting for the next episode to come out. Netflix let's me pick the next movie whenever I want to watch it. It's just a preference thing I guess.