I was a contractor for a major IT company via PlanetPro for several years and it was very easy to work with the staff in terms of getting questions answered and the support I needed. Benefits were great and week to week was smooth sailing.
Cons
Some of their online HR systems are clunky to work with and take a while to understand. In the end I was disappointed that they didn't go to bat for me of their own accord for an overdue raise over the years, or provide me the "thank you" gift certificate I was promised.