Honestly, if the bench is going to sit in direct sun day after day, recycled plastic will outlast wood in almost every case. The sun is harder on wood than people expect: UV rays break down the lignin that holds wood fibers together, which causes fading to gray, surface checking, and eventually fine cracks. In a hot, exposed spot, even a good wood bench needs sanding, sealing, or oiling every year or two to keep it from becoming rough and splintery. If you skip that maintenance, many softwood benches start looking tired within a few years, and even hardwoods can weather badly over time.
Recycled plastic, usually HDPE, is different because it is made with UV stabilizers from the start. It does not absorb moisture, so it will not rot, warp, crack, or splinter the way wood does. In direct sun, it can fade slightly over many years, but structurally it will easily last 20 to 25 years or more with basic soap-and-water cleaning. No sealing, no staining, no sanding.
The trade-offs are mainly looks and heat. Recycled plastic benches have a clean, consistent finish, and some are textured to resemble wood grain, but they are not identical to real timber. On a very hot day in full sun, dark recycled plastic can get uncomfortably warm to sit on, while wood usually stays cooler. Choosing a light color helps a lot.
If you really want real wood, go with teak, ipe, or shorea. Teak is the best wood choice for full sun because its natural oils help resist UV damage and drying. It will still silver over time, and you will need to clean and oil it occasionally if you want to keep the original honey color. Even so, a well-maintained teak bench can last for decades.
So, for the longest life with the least work in direct sun, choose recycled plastic. If the look and feel of real wood matter more to you and you are willing to maintain it, choose teak or another dense, oily hardwood.