I would prefer misting the soil and seedlings. Water tray isn't really reliable for me. First, more media is needed so that the water tray does not flood/waterlogged the soil. Then, there's the issue when you need to remove the water tray eventually to prevent root rot for the seedlings(unless you are using a pot or a few inches deep soil). The water level needs to be mantained too, not too much and not too little. And lastly, mosquitoes larvae have the tendency to grow ALOT in water trays for me, so now I hold a grudge on the effectiveness of water tray
On the contrary, spraying is more safer. The only risk you will have to face is media drying due to insufficient sprayed water. And, it's not even time consuming unless you have a hundred of germination trays
. Misting also kind of simulates a raining envrionment for the seedlings which I believe is beneficial for the plant (note that this is just my opinion and observation, it might not be true!).
Therefore, I would prefer spraying!