I once resorted to using ellipticals for a few weeks due to injury.  The elliptical machines were lower impact than what I normally do.  One gym had Precor machines that seemed comfortable and well built.  The other gym just had a cheap machine with no electronics.  I could get a reasonable workout from either one.  The important thing for me was to have a television mounted on the wall, or anything to watch other than the wall.  Having a fan also helps if it's hot.  The Precor machines seemed to be very popular.  I had to show up at some odd hours to get enough time on them.