What 3PAR OS version (and DDS version)?
My general thought is "what is the customer looking for?"
If performance is the number one priority, then everything goes thin.
If they are at a point where they think they might run out of capacity before the system has reached the end of its lifecycle and cost is a factor, then go data reduction (dedupe or deco).
If the customers previous storage array was a small system with 30-40x 10k/15k drives, then you can probably do whatever you want with the 3PAR and it will never perform less
Just keep in mind. Any data reduction technology requires you to have a little bit more head room in the system as it will have to do more cleanup in the background. If you're running out of capacity and need to take steps to free capacity, you usually need both more capacity and more time (resulting in even more capacity) than if you were doing simple thin (of full) volumes.