Good news, this enhancement is actually included in our next release, due out this month:
The default Task Type is changing to Fixed Duration for all Create Task options (Quick Add, Add Task and Gantt Chart), and it will actually remember each user's preference, so if you happen to prefer Fixed Work planning, you'll just need to change it once and that will persist for all Tasks you create in the future. So, rather than it being a globally-defined setting, we're changing the default task type to the most frequently requested type, then we're allowing individual users to set their own preference if it's different.
It will be a bit of a learning curve for users who have had to learn how to work with the existing less-than-ideal Create Task structure, but I think you'll be pleased with the changes.
Cheers!
-Erik