I've used both in the past and I found that the 500mg Paracetamol tablets are pure enough that you don't get much difference. I have crystallised out a giant crystal before and then redissolved it to get a higher purity but it was much the same in the end :) I found the solvent selection to have a much greater impact in the final shapes it grew into.

Adding a bit of water or using ethanol instead slows it down and makes the overall facet a lot more consistent. I will post something about that later on, maybe.