The Halide lights produce between 65-115 lumens per watt which is a measure of the efficiency of the bulb, or how much light you are producing for the amount of electricity you are using. The Sodium lights produce light that is very bright and concentrated on the yellow to red side of the color spectrum. This color is not as balanced as the Halide but makes up for the lacking of a balanced spectrum in the amount of light given off by the bulb. The Sodium bulbs produce between 97 to 150 lumens per watt which is much higher than the Halide bulbs. The Sodium bulbs are superior in life expectancy and efficiency while the Halides a superior in spectral distribution so your decision will be based on what is more important to you.
Many people switch between bulbs for different stages of growth for a couple of reasons.
First of all, Sodium bulbs have been known to make some plants grow leggy and stretched out because of the yellow to red spectrum that they give off. Metal Halides tend to keep these plants tighter with less space between internodes. So some growers use the Metal Halide lights during vegetative growth to keep the structural growth of the plant nice and tight. But they switch to Sodium lights when the plants begin to flower because the Sodium lights produce so much more light than the Halides. Even though the Sodium's do not have as good a spectrum as the Halides the intense light that is put off by the Sodium's aids in flower development and fruit set.