The best material to use for an automatic driveway gate is dependent upon your certain preferences and what features of the gate are most important to you. The most common materials used for automatic driveway gates are wood, iron (or other metals), and composite material. 
Wood is especially useful for achieving a greater level of privacy. Wood gates also provide a more natural look, so depending on the style of home or the atmosphere you are trying to create, wood might be the best material to go with. Wooden gates do have to be maintained with either stain, paint, or a different coating to protect it from rot and bugs. The price of the materials depends on the quality, density, and other features of the wood.
Metal gates also provide a unique look to the outside of your home. They are sturdier than wood gates but they also tend to provide less privacy as well. Iron gates usually have poles or panels that are spaced further apart, which creates a gate that provides a clear view into the yard and of the house. Iron gates can be more expensive to upkeep in that an iron gate can rust and break. If it does need repairs both the materials and the repair services are more expensive than both wooden and composite gates.
A composite material driveway gate can provide just as much privacy as a wood gate can. Composite material is much cheaper than both the wood or iron options while being much lighter than the other two as well. The composite material itself is white and can be installed as is but would most likely have a more wood like appearance when painted. This material is the lightest compared to iron and wood, but requires little to no maintenance as the material is waterproof, does not rust, and will not get eaten by ants. The material may crack, however replacement parts and material are generally cheaper than both good quality wood and iron.
But the best material to use for an automatic driveway gate is very subjective. You determine which one will work for you. You really want to take into account how much you want to spend on materials, installation, and maintenance, as well as the overall look you're going for and that will help you decide what's going to be the best material for you.