I like perlite (equal weights water and perlite). Because it allows for more airflow around the eggs and the white color makes the egg quality easier to see (calcium content during incubation- sometimes changes if the eggs are poorly calcified which gives clues about state of husbandry). Vermiculite doesn't allow as much light around the eggs, making them darker and making egg quality more difficult to ascertain.
I sometimes use vermiculite though. Mainly because I have to drive 90 minutes to get perlite without miracle grow in it. With vermiculite, a few times over the years (out of thousands of lizards so the chance is small) I've had hatchlings get a mouthful of vermiculite as they are hatching, which kills them of course. So if you go with vermiculite, try to get the course material.
I haven't really noticed a difference in successful hatch rate between either substrate.
When I was young, I once hatched a bunch of blacksnake eggs in a coffee can with damp paper towels! I've known breeders who use dirt or sand also.
