In this paper, a randomized, controlled study, 53 patients had Botox on one side of the face, and Dysport on the other. They were then followed for 150 days to see how they did. The usual conversion ratio of 2.5 units of Dysport to 1 unit of Botox was used, in equal volumes of solution.
Results: no difference - in this trial, both sides were totally comparable and equal, from day 2 out to 150 days post-injection.
As I've said before, it's a bit of the "Coke versus Pepsi" situation... pick your favorite, as both Botox and Dysport are both equally effective. And of course, we offer both here at our Orlando office.