Obviously you can see my bias (by the way, finding images without the word "****" in them was very difficult). I find that the Star Trac seems to be the best. They hold up better than the Schwinn and the Precor and they aren't susceptible to friction pad squealing, which is a real problem with the Schwinn. Ergonomically, the Star Trac seems to be the most adaptable, plus as an instructor they are the easiest to set up for new people.
Precor is probably my second choice. They don't seem to have as much of a problem with sweat dripping on the wheel causing binding, which can be a problem with the Schwinns and the Star Tracs.