I am also looking into fencing options as we are in the middle of a pending purchase on an acreage. From what I have found and what I have experienced is the following:
Fencing needs to provide both a physical and a psychological barrier. It is better that the horses perceive the fence to be a solid barrier than they physically test it. Wide bands (4" or so) of flat, re-enforced PVC fencing in an obvious color will do this as will rails or boards.
Electric fencing is very effective, but the type of conducting material is a consideration. Visible, flat braided strands are better than rope or narrow strands. They will break relatively easily, but they won't cut your horse. Electric fencing used with either step in plastic posts or PVC posts is also very mobile and a great way to subdivide your pasture. This will allow you to preserve and manage the grazing space by rotating the areas your horse are out on.
Galvanized wire or square field fencing with larger squares can still be dangerous. I've had more than one horse put their feet through the fence pawing at the other side and end up cutting themselves quite badly.
When building a fence, try not to give your horse reason to reach through it. Keep the perimeter mowed, and ensure their food supply is well managed so they can graze (safely) most of the time.
I consider T-Bar fence posts to be temporary. Treated wood posts about 5-6" in diameter are better and safer. Make sure your posts are put in the ground deep enough or they will work themselves out. Also, re-enforce the corners well with braces. The post themselves can range from 6-12' apart, depending upon the type of fencing you intend to use. Buy the best posts you can afford, as this is the part of your fence that will remain in tact for the longest period of time.
Regardless of your fencing, your horses will need something to chew on and something to rub on. Make them a "scratching post" that is accessible so they don't use the fence for this purpose.
If you are pasturing horses in a smaller area or a region where grass is seasonal, consider including a "sacrifice" pen where you can contain your horses for winter feeding. Their hooves will do quite a lot of damage to a small pasture, especially when wet, causing you to lose good grazing space.
A mixed materials fence is ideal and reasonably cost-effective. I am considering a treated pole top rail as a physical barrier, with two or three additional strands of either PVC coated wire or electric tape underneath. As I can afford it, I plan to add the second and third rails with time.
Lastly, purchase good quality gates with good latches / fasteners. Metal tubular stock gates are ideal as they also come with a chain fastener. Make sure you have gates wide enough to get a tractor through in case you have to harrow, till or re-seed your pasture at a later time.
I hope this helps.