probably most common on the big island I'd imagine, due to the peak there.
I don't really have a proof for this, but it seems like atmospheric charge mostly builds up due to charged dust and other particulates being blown up from the ground and into the upper atmosphere. Since this requires wind + a lot of land surface area for particulate capture, it would follow that islands wouldn't get a lot of lightning.
But now I'm wondering how lightning in seaborne hurricanes and tropical storms originates.