Several types of lighting serve aquariums with life plants; each has pros and cons. No single form of lighting is "best" for a planted tank. You'll want to know about each kind of lighting to determine which is best for your setup according to what species of plants you keep.
Standard fluorescents are the basic lights found on most aquariums. They have low cost going for them, but many other types of lighting kick out more powerful light. Generally, you want to use 1.5 watts to 5.0 watts of lighting power per gallon of aquarium capacity to light a planted tank. With standard aquarium fluorescents, you should probably lean toward the high end of this range to ensure that your plants get sufficient light to thrive.
Several types of more powerful fluorescent lights exist. "Powered compact" or PC fluorescents and T5 lights are powerful fluorescent lights that kick out more lighting than regular aquarium fluorescent. These may be a better choice for most aquarium plants since they produce more powerful light that more closely resembles the sun's rays. However, these lights cost more than standard aquarium fluorescents and require special -- aquarium talk for "more expensive" -- fixtures than their standard fluorescent counterparts.
Metal halide lighting produces stronger light than advanced fluorescent tubes. Metal halide lights penetrate water very well, making them ideal for deep aquariums, since light attenuates in water. The biggest drawback to metal halide lights is that they get hot. You may have to set them up with cooling fans to keep the aquarium from overheating. In a wide aquarium, you may need more than one of these lights to adequately cover the tank.
LEDs are the latest innovation in aquarium lighting. Right now, these lights tend to cost a lot up front. However, the cost is dropping as the technology matures. At the same time, they cost much less to run than other types of aquarium lighting. For example, both florescent -- standard and advanced -- and metal halides need to be replaced yearly to maintain their output. By comparison, LED arrays can run for at least 10 years without replacement. Additionally, LEDs need less electricity than other types of lighting. An LED array needs a quarter of the power that a metal halide light requires to produce equal amounts of light.