Lets do some maths.
Contract A starts Monday. Easy work. Roughly 120 hours at a rate of $100 an hour.
Contract B also starts next week. Tougher assignment with a lower hourly rate ($75) and only half the amount of hours.
You can only take one. Which do you take?
The answer: It depends.
In the business world, everyone is paid in two coins: cash and experience. Take the experience first; the cash will come later (Harold Geneen).
Work is rarely just about money. In the end, the job that pays the most may not be the most rewarding; long term is often better than short term.
Quantify – how much fun, visibility, happiness and experience will you gain out of the work? You may ultimately make more money by taking lower paying contracts.