Solidworks and Zbrush are two totally different modelling packages, so if your more into your organic modelling and characters etc then go for Zbrush. I can use Creo/Solidworks pretty well for all kinds of mechanical things, with parametric modelling...however because of my Parametric mechanical mind I found Zbrush sooooooo hard!! There are loads of tutorial videos online though, and as suggested above go for Sculptris first which is a great little version of Zbrush but is free.