This is a common question asked when scheduling a task in Project. I would say the question is not about “best” task type but about “right” task type.
If you are scheduling using Project 2010 or later version, you should be aware of the new task field – Task Mode. If not, please read this article – https://support.office.com/en-us/article/task-mode-task-field-3b185518-0e9a-4774-ba51-7b8d191bb84a – before continuing.
First, let’s learn this formula: Duration = Work / Units. That is duration of a task is equal to total effort required to complete the task divided by the number of available hours resources can spend on the task. For example 40 hours task with two full time resources (who work 8 hours per day) will take 2.5 working days to finish the task.
Second, for a given task prioritize which of the three variables – duration, work and units – is most likely to be constant. The word constant doesn’t mean it is disabled. The word constant signifies the value of this variable will not be changed by “Project” when the values of the other two variables are altered.
Third, how to prioritize between these three variables? Ask what is this task all about? What is driving this task? Is it time or effort or people? What are the constraints on this task? What are the risks associated with this task? Answers to these question will help you to decide whether the task needs to be “Fixed Work”, “Fixed Duration” or “Fixed Units”. Microsoft has published a detailed article explaining the different scenarios demonstrating how to change the task type – https://support.office.com/en-us/article/change-the-task-type-for-more-accurate-scheduling-b0b969ad-45bc-4e9e-8967-435587548a72
Fourth, this is something no often documented. The task mode will the change the behavior of Task type. The above support article and formula works for auto-scheduled tasks.
What about manually scheduled tasks?
First, manually scheduled tasks get task type from Project Options. Unless you have changed it, the task type defaults to Fixed Units.
Second, Gotcha! You can’t change the task type of manually scheduled tasks 😦 as I think the primary purpose of manually scheduled task is to create a place holder for vague high level tasks. Yet if you feel task type should be enabled for manually scheduled task, vote for this idea – https://microsoftproject.uservoice.com/forums/218133-microsoft-project/suggestions/36858493-allow-task-type-to-be-changed-for-manually-schedul – in User Voice.
Third, Fixed Units and Fixed Duration works correctly for manually scheduled task but work will not be fixed for Fixed Work. If you change the duration of a manually scheduled Fixed Work task, the work of that task will change.
I am eager to know what method you use to select the right task type. Share yours as comments to this post. Happy Weekend.