It depends on what you need. I use a solid x-stand in my studio, where I'm sitting down, or if I'm going to jazz gigs, and am only taking one keyboard. If playing a show with a rock band, however, I massively prefer to stand up, and an x-stand isn't stable enough, and generally can't even reach. So I use a Z-stand with an extension so I can get my boards at the same relative height to my hands as if I were sitting in front of them.