Your choices in line posts for electric fencing should be a major consideration for you. Line posts costs are a big part of your cost per foot of fence. They also represent a high percentage of the maintenance that may be required for the life of the system as well. Sometimes the appearance of the fence is a priority, in which case you may be willing to pay more for a line post that not only performs functionally, but has added eye appeal as well.
As we travel to different parts of the country, we notice that geographic location influences choices as well it should. Driving through Texas you may see a lot of cedar picket line posts, spaced close together. Local fencing folks explain that in their area cedar posts were inexpensive and plentiful. With an abundance of forests and sawmills in the pine forest of the Southeast USA, they also use a lot of wooden line posts. The use of wood line posts is a great option if you have local resources for them and your soil types allow you to auger or drive them in. The equipment you have on hand may also have a bearing on your choice of line posts.
When using wood posts just remember to use good quality insulators and consider the longevity of the different wood species. Black Locust makes a good wood post in the east, and Hedge (also called Osage Orange or Bois DArc) in the mid-west. Hedge posts tend to be very crooked, which we like to refer to as character. Because of the wood density and consistency of Hedge it absorbs very little moisture therefore conducting very little electricity, not to mention adding tremendous longevity. Even stapling electric wire directly to Hedge results in rather insignificant energy draw from the fence. Its a favorite choice in our area for end and corner posts.
It may be apparent that we are not in favor of using steel posts in electric fence systems. We feel that steel is the enemy when it comes to electric fencing. A steel post is basically a ground rod. However, sometimes it is necessary to use T-posts and in that case we recommend that you use the best insulator you can to help keep shorts at bay. Black or dark green insulators will have carbon added which is a natural UV stabilizer. Yellow insulators dont have the UV stabilization and when the sun dries them out, miniscule cracks form. When those cracks fill with moisture it causes a short. The other problem is that if the wire is knocked off the insulator and touches the post it results in a rather major short.
It is our opinion that self-insulated line posts are your best choice for electric fencing. Powerflex posts, and fiberglass sucker rods are all non-conductive. Some fiberglass rod posts are treated to reduce the amount of slivers involved with them, some are not. You will quickly become aware if you happen to have the ones without coating. Fiberglass is slicker and hard to drill in the field, so you need to purchase pre-drilled posts or drill them yourself in the shop. Powerflex posts hold in the ground very well and are easy to handle. They can be drilled in the field very easily and with little to no run-off. With these self-insulated options, the fence wire is generally attached to the post with an inexpensive clip or cotter pin.
Powerflex and fiberglass posts both have some flexibility and they do allow hi-tensile fence wire to be springy and bouncy as it is intended to be. This flexibility allows for a lot of forgiveness regarding wildlife damage and tree limb problems. We like to think more flexibility and less fortress. Remember that with electric fencing, the electric shock is a psychological barrier rather than a physical one.
In summary: by using a non-conductive line post, you will be assuring yourself of much less maintenance down the road. Looking for broken or cracked insulators is a very time consuming job.