This is really a personal matter and usually based on space and your personal likes

I personally like the fiberglass rods. But I often pack 30-40 of them into remote meadows in wilderness areas. I find them lightweight and easy to push in the soft soil of a meadow. You may prefer something stronger than can be pounded or driven into hard soils, depending on where you camp.  My horses respect a hot wire, So I don't need a lot of fence. 1 strand of poly string is enough to keep my horses in the meadow grazing. I highline at night, So my horses are only in the hot wire enclosed area during daylight.

I also usually just fence off a large circle, So I have no corners that require extra bracing. If you fence square areas, you may want something stronger for the corner post.

I made 4' high PVC (3" diameter) poles with 24" of conduit (3/4") strapped at the bottom, 12" for inground and eyebolts to string clothesline.  My horse doesn't even test it for current.  However, I have a trail buddy whose horse went right thru it the first time.  We modified the same poles with conductors, electrabraid and solar charger.  It works great.  If I get to a camp with hard ground, I pre-hammer holes with a same size steel stake.

My square pens are adaptable to be bigger or smaller spaces but we usually keep them 12x12