Doug:
There have been a number of discussions on the board about post drivers. Those who have them swear by them. They put the post in straight, with no need to fill around it or tamp. They therefore are much faster, and the posts more firm. I have never used one, so got the auger, which was cheaper, isn't limited on pole height, and can also make holes to plant bushes, etc. The most time consuming process when I do fence work, not to mention the most fatiguing, is filling and tamping. I'd love to have a driver, but most of my work is a couple of posts at a time for repairs. The one 78 post run will be the longest I need to do for quite some time. If another long run needs to be done, I'll probably get the driver.