Completely down to personal choice
The spots are more directional light and when trying to replicate moon and sun it is nice to have an area of high intensity instead of an even spread of light, just like in the wild, we have all seen the moon light reflecting off water and what effect it gives. Also if you have two spots you can bounce the storm effects more randomly across the surface.
if you go for two spots have one either end, and pitch to meet at a central point, this will also create a good light spread across the tank but still give you that focal point.
Sticks are great too, they will give amore even spread of light.
My personal choice is spots, but as I say its all up to what you want to acheive really.