That’s a loaded question and for anyone to answer it you need to tell us more about your intended use and expectation from the use of these options. Some insight into your company or the tell us what industry is helpful. This is a very customized decision based on how you plan on using any of those options.
In QuickBooks Online (QBO), the Project feature works like Job Costing in QuickBooks Desktop. This feature helps you to be organized and track all moving parts. You can also use sub-customers, to track your projects and job costs depend on your preferred way of tracking.
You might create sub-customers if:
Use sub-customers for members of teams or leagues.
Homeowner Associations and Property Management companies often use sub-customers for individual properties.
To help you decide which best suits your situation, you can take a look at these articles for guidance: