It all depends on what kind of model you’re working on. Both workflows are good for different things. Sculpting is generally better for making complex organic shapes (like characters or animals or lumpy rocks) and doing a “low poly version” first is often much faster for man made objects (that you can break down into simpler shapes) like pencils or chairs or houses.
Also ZBrush is really good and there’s so much amazing art done with it, but it’s a pain to learn and indeed quite expensive. There are sculpting tools in most of the popular 3D modelling programs now too though (Blender, Maya and Modo have them) and there are a number of other sculpting programs as well, like the free Sculptris (pretty basic, but hey, it’s free) Mudbox (but it’s from Autodesk, so it’s only got a 10$ a month subscription and you can’t buy it) and 3D-Coat (which is about half the price of ZBrush, does a lot of things really well, but doesn’t have some fancy features like FiberMesh) I personally use 3D-Coat for sculpting, retopology, UV mapping, baking and texture painting. I think they all have free trials though, so do try them out and see which ones you like before you buy something you don’t like.