Wood pallets are somewhat traditional and are also easy to find for sale, but many facilities today are also using plastic pallets, either in addition to traditional wood choices or instead of them. If you need to buy pallets for your shipping, warehousing, or manufacturing facility, note a few considerations that might help you make the choice.
Wood is probably much more eco-friendly than plastic; while plastic can be recycled, this process involves heat to melt down the material—and this heat means fumes and other such pollutants. Wood can simply be cut or otherwise easily fabricated. Even a wood chipper that turns old wood into mulch may produce fewer pollutants than the process used to melt plastic.
Plastic is typically more durable than wood, so plastic pallets may last indefinitely no matter their use. This is obviously important to consider for heavier items you might transport or store, but also for long-term storage. Wood may absorb moisture over time and, in turn, become soft and weak. Even for pallets only used for storage, if you need to use them long-term, plastic may mean more stability for your items and less chance of soft wood pallets giving way or breaking altogether.
Even when coated, wood pallets can still absorb chemicals as well as bacterial agents that make them very unhygienic. In a warehouse or storage facility, there may be rats or mice or other pests that leave droppings or spread germs near the pallets and wood is more likely to absorb these contaminants. This can make them a poor choice for shipping and storing foodstuffs, chemicals, and other such materials; one small leak in a container and the materials stored can be easily contaminated. However, plastic is more hygienic as it's not likely to absorb bacteria, grease, chemicals, germs, and other such agents, keeping sensitive materials safer during storage and shipping.
Plastic pallets can often be found in a variety of colors, which may be necessary when shipping overseas; the colors can designate certain hazardous materials, chemicals, and so on. For your own purposes, however, you might choose colored plastic pallets for easier organizing and storage; they might denote different customers, different materials being stored, or areas of the facility where items are to be stored.
Typically wood pallets are more affordable than plastic and are the better option for shipping. You don't need to worry about having the pallets returned to you in order to recoup the cost when you choose cheaper wood pallets.