Most people in my locality use plastic pegs, its hard to find wooden pegs unless they be custom made. I am currently working in a busy laundry and we use barbed wire to hang clothes. Unlike pegs, we don't have to worry about replacing lost or broken pieces which saves on costs.
Definitely plastic. Wooden gets rotten and becomes darkened and ends up soiling clothes. No matter how much you care for them, it might rain and it becomes soiled. With plastic pegs, all you have to do is just pick them in and out. No rust, no rottenness, no soil.
Wood is more sturdy but it will get wet just by pinning the wet clothes, right? So I think the better and cheaper choice would be the plastic clothes pin. We have always used the plastic kind ever since, and from what I observed, they tend to last for many years, I say around 5 years or more.
I bought both and I prefer wood clothes pins because plastics breaks fast. Wood clothes pins seems to be more durable and if it starts slipping all you have to do is put the wood back into the metal part and it starts working again. Wooden clothes pins goes on sale too so you can get a good price on wooden clothes pins.
I prefer wooden clothing pins. From my experience, plastic breaks after some time because the clothes that it pins are wet, thus eventually degrading the quality of the plastic. The wood also has better grip in my opinion, and it definitely has a longer lifespan compared to the plastics. Nothing is more annoying for me that plastic pins breaking while you press them.
