What kind of concrete is best for fence posts?

I need to have a 70 ft. long fence replaced. I’ve contacted several fence companies about the job. I’m puzzled about the different kinds of concrete that are claimed to be the best for the job. I’m talking about the concrete that you set the fence posts in.

One guy says that he uses quick-setting concrete because it’ll set before the posts get a chance to wobble. (A pretty strong wind usually comes through this area around sunset.). Another says no, that regular concrete is best, quick-setting is like cutting corners. Still another says he uses pre-mixed (is this the same as quick-setting?). I’m sure there are other kinds. So, I’m confused.

What do my fellow jellies say? Would appreciate your advice.