Grossly, insanely different PD strengths

[Archonsod]

Not really. I never bother with PD for Caelum (no point, Caelum's troops need scripting to be any use), and it's rare I put in more than four or five PD with most nations.
For those wondering, I find it more effective than the traditional 20 PD for putting off players looking for an easy victim. Just make sure they think the cash you've saved has went on your army instead

Nations with good PD, such as EA Abyssia, tend to use it more because it can do a decent job. This can be a disadvantage as much as an advantage though - a couple of times I've foolishly invested in PD when actual troops would have been a better use of gold.