Simply the best!!
A few weeks ago I was contemplating whether or not to purchase ZBrush or Mudbox, after watching tuts. on both programs and watching a video with Hollywood effects wizard Rick Baker mention how he loves using ZBrush, it was the obvious choice. I am a burgeoning Poser content creator and ZBrush is MUCH more Poser friendly than Mudbox for making morphs for characters / props. The pixologic website has tons of free content to download for ZBrush (alphas, Matcaps, textures etc.) and there are tons of great tutorials to get you started on Youtube or Pixologic, you won't regret the purchase, trust me!!!