If the stainless is thick it probably wouldnt matter which one. Cast iron seems to hold heat more consistent so if you get the temp and timing down it is more repeatable if you are a precise person. Cast iron could impart other flavors of goodness depending on what was in the pan before.
Discussion
I went with cast iron and whipped through them super quick. I think I was able to cook them hotter with less sticking on the cast iron.