Metal Halide lights are extremely powerful and you might need a chiller to keep the tank cool, they give off an extreme amount of heat.
Actinic lights are used for aesthetic purposes and for coral growth, in the open ocean, the deeper you go the more light is absorbed by the water, the actinic lights mimic the effect of the blue hues that penetrate deeper into the ocean.
The zooxanthellae in corals use the blue light as a food source.
Metal Halides mimic the intense power of the sun on a sunny day. If you have a deep tank then it might be beneficial to go with the metal halide but your 14K coral grow will probably be sufficient and less of a drain on your electricity bill.