What is better for lighting fixtures low voltage, or line voltage slash high voltage.

There are different factors that would push you to buy both types of lighting in different situations. Some of these factors are cost, longevity, energy savings, and design.

As far as cost between low voltage, and line voltage fixtures the low voltage tend to be more expensive because they need a transformer. Low voltage tends to be more specialty lighting which also can drive the cost up.

The Longevity of low voltage vs high voltage is roughly the same so take that out of the equation.

Energy savings between low and high voltage is all about wattage. The same wattage bulb in low, or high voltage use the same power. For the low voltage bulb of the same wattage to a high voltage bulb would have more amps- volts x amps = watts.

The real factor in choosing between low voltage and high voltage is the location and design aspect. For cabinet lighting I like high voltage because there is no transformer to hide, and low voltage wire needs to be run around the cabinets and not inside of the wall by code. For track or pendant lighting either is fine, sometimes the low voltage have the cooler fixture designs. For outside lighting the low voltage is supposed to have better options, but this should be researched.