I got it from my wife's policy

Med insurance ($10K), uncomped hours (200 hrs = 10 holi + 15 vaca), and 401K ded + matching are the main difference between salary and contracted rate, plus short/long term disability, life insurance, and others. I work on all holidays to make more money and my staffing company get me other insurances (no discount), and 401K (no matching of course). If you are single, take the salary and ask for a little raise or bonus(on paper). Never discount company benefits these days when health cost is so high.