I used (struggled) with Poser 6, then 7 for about 4 years before moving to DS.  Now I'm a Studioaholic - I use it much more than I ever did Poser. One of the best things about DS is being able to locate products easily .  It used to take me ages to scroll through a list of names to find what I wanted in Poser, and as my runtime grew it started to take a seriously long and frustratng time! In Studio, because it's easy to change the names of products on the fly and because you can see images of the products, it's easier and faster to find the things I need to start being creative.
There are lots of other great things about DS  - such a using aim-at lights - again no guesswork - you know exactly where each light is pointing. It also has some seriously cool plug-ins available. Occasionally I open Poser for the cloth room and to use WW  before the latest stand-alone version.  I've never found a use for the Faceroom.  For me DS wins hands down.