Keep in mind that it is what the cattle perceive as being impenetrable, not you. That wire may stop them but an excited animal cannot see it and may end up causing injuries. I have seen many old rotten wood corals hold cattle only because the cattle did not know they were rotten. I have given height to corals, stopping jumpers, with the addition of PCV pipe at the top.
Going back to the original question; Metal has it's advantages but only if it is heavy metal. By heavy I mean oil field pipe. The stuff made today and sold at TSC and the like, in my opinion, is junk that will rust out in no time. Oil field pipe has enough thickness to last. My pipe pens were originally erected in the 60's. Except for needing grease they are as good today as the day they were first erected. The draw back to pipe is that it has no give. When cattle hit it hard it can cause injury. The other thing is that it can become hard to climb quickly when you get cow crap on the bottom of your boots. If you make a mistake in design pipe can be expensive to change if you do not do it yourself.
Wood corrals do not have the longevity of good drill stem. Wood is much more elastic and easier on the cattle when they hit it. Wood because of it's width looks to the cattle that it is more substantial so they resist the urge to hit it. Cattle strange to the corral seem to work easier in wood corrals, in my experience. Wood is also easier to get over when the need arises, running from the cow or just needing to get over for what ever reason. Wood is also much easier and less expensive for the average person to redo if you find out you need to change something.