I've *heard* that Leopard Geckos should get the "calcium only" powder, as they are nocturnal, their system does a good job getting D3 out of their prey items and further supplementation is not necessary.
Vitamin D3 can be toxic in high quantities.
Then again, I've have yet to hear about a single case of D3 toxicity in leopard geckos, or any other lizard for that matter.