london course ms project - Task types and effort driven tasks

Hi,

When entering tasks - is this the point where you should decide whether your task is fixed unit, work or duration and after the decision whether the task type should be effort driven or not?

What are the common factors in deciding how to make this decision?

OR do you use Project defaults of fixed unit and effort driven and wait until you assign resources and then are prompted to choose a task type with warning triangle ?

I know that adding resources to a task, changing its type and deciding whether it is effort driven or not are ways to reduce scheduling conflicts but is it correct that deciding task type is too late at this stage.

Thanks for any help
Narinder