Fixed Price vs. Time & Materials

If the choice were mine, I'd go with fixed price contracts as often as possible. They can be crafted to reflect the buyer's value of a project (rather than just asking for a fixed daily rate) and there's the option for super-profit if you deliver the project for less than you anticipate. Of course the planning that goes into the bottoms-up estimations that lead to successful projects has an associated cost, but it does mitigate the risk you won't deliver on time.