Electrical Fence

What is the best electrical fence to buy? I've seen regular wire. I've seen a coated, white wire. I'm not sure what's best or most cost effective.

I've been looking at electrical supplies trying to figure out the average cost per acre for fencing in pasture, but I have no idea. It's a definite necessity because my half Draft will lean on the fence and push her boundaries if she's allowed to.

It only takes one zap to remind her why she shouldn't do that. I know I shouldn't think it's funny but when she's leaning on the fence and it's turned on, it's funny watching her take off away from the fence. I'm a bad horse mommy.