The types of risk mentioned in the original post of this thread, financial risk, schedule risk, resource risk, and quality risk, are all important components of the project. It is ideal to minimize risks so the project can progress according to the plan, in all aspects. It is difficult to say which type of risk is most or least important. For example, if there is little financial risk, but great resource risk, then the project success is in jeopardy. The type of risk that is present in the project and is the most difficult to overcome, is the most important risk. It is project specific, and definitely on a case by case basis. If there is a financial risk, and the stakeholders are not willing to contribute more funds, then it is detrimental. If there is a quality risk, this will not bode well for governing bodies such as the FDA, and can put the company in jeopardy. If there is a scheduling risk, where there is no acceptance for late deliverables, then the project is not accepted. 

While all four risks play a critical role in project success, schedule risk is often the most present due to factors like unexpected delays, resource availability, and scope changes.

However, I think quality risk is because every phase, design, development, testing, and production requires strict quality control to meet standards. Failure in quality can lead to product recall, safety problems and may not be readily recovered. The seriousness of these risks does differ by the nature of the project. Unlike schedule or resource risks, quality risks can have long term consequences, affecting user safety and regulatory compliance.