On VividCams you decide how much you want to charge per minute (typical rates are $1 - $12 a minute). You receive a percentage of every dollar billed to your chat.
Vivid is just Streamate in another package. I've found them to be a bit more helpful, and the members area for girls to check out videos, get news and learn about contests is pretty cool.
I have been with Vivid for about 5 months. They are amazing. We do contests every month. They have been extremely generous and even provided us with Video's of camgirl tips.