Hourly or Fixed Bid Contract Work?

I've long wondered what is the best arrangement for paying contractors: hourly or fixed bid. Pay hourly and they could work slow or worse, be learning on your dime. Pay fixed bid and they could work too fast, and cut corners. As an example, the electrician who installed about 40 recessed lights for me finished in about 2.5 days. He estimated it would take him a week. I paid him a fixed price and he made some serious dough for the 2.5 days he worked. Another contractor estimated 1.5 weeks to complete the job. I have to admit I was a bit peeved he finished so quickly. There were some quality issues with his work but nothing too bad. Similarly, I paid a handy man hourly to do some work and he treated me like a paycheck.  But it took me a while to catch on. At first he worked fast and did great work. Then he slowed down and seemed to always finish the job right around 5 - how coincidental! With hourly, it seems the burden falls upon the homeowner to do a lot of the planning and oversight, for example, ensure materials are available, and arrange the work in the most efficient manner. Since you're paying hourly there is little incentive for the contractor to plan well, or work quickly. I didn't like this arrangement much since it required more work on my part, and I got really stressed when projects took longer than estimated. The fixed bid seems to be a good option for work that is easy to estimate. A couple examples that come to mind are painting, tile work, installing floors/doors, removing a tree etc. These are all tasks that professional should be able to estimate accurately. If they are unwilling to go fixed bid, that could be a red flag that they're not confident in their trade. The problem for me, is, like most homeowners who don't have home improvement experience, how to analyze a contractors bid. For example, I have no idea if one week is reasonable to install lights, or tile a bath. It helps to have a general contractor resource who can review bids check for fairness. Multiple bids are usually a good mechanism to root out high ball bids, but may not always work. Scope is an important issue with fixed bid, for example, a task to repair drywall imperfections can be vague, depending on how obvious they are, and without identifying each issue with tape (work on your part), the end result may not meet expectations. I like to ask fixed bid contractors how much they charge per hour incase something else comes up that is not in the scope of the bid. Fixed bid will surely limit your risk, of slow work or inefficiencies, but you may end up paying a premium since the contractor is taking on some risk of the unknown. A confident contractor however should be proficient at estimating work. If you have a good trust relationship with a contractor, who is very competent, hourly may work well. I think the bottom line is to select really good contractors that know exactly how to do the job and can problem solve when the unexpected occurs.