What's better for fence posts - wood or metal tbar?
If you can get black locust posts, they tend not to rot, or not for a long time. Most other wood posts rot, and rot faster in concrete, IME. Concrete offers no benefit over a properly tamped backfill of soil, in general. Steel posts rust, how fast depends on the climate (well, so does how fast wood rots, for that matter.)

Livestock may be more prone to chew on wooden posts, depending on the stock (swine, I'd suppose, by your username.) Pressure-treated posts can be bad for that reason.

Other than that, the choice comes down to cost, usually.