I have the HVX200 and have used/rented the other cameras.
First, using the 500 or 200 you have to get your head around the P2 workflow, which means buying more hard drives then you can ever image. It is not a horrible thing just takes more thought then, "how much tape do I need to bring"
I'm a firm believer in buying the most camera you can afford (notice that I only have the 200) and then I rent cameras when I feel the 200 is not up for the task. I also match cameras as much as possible for multicam shoots. In the end I think you either spend too much time in post making all the cameras match or you dumb down the better cameras to match the lower one.
But in one need more than a single camera for different jobs and they very in budget these two options are great choices. They all have their places and strengths, but less expensive cameras will alway be a compromise so the question goes back to you, can you (and your client) live with the compromises. Most of the time the clients budget answers the question for us.