Well from my own experience using both, much people say that Gmax is really challenging to learn whitch it is... However, when I used FSDS it was and still is challenging for me to learn and use the tools effectiently to develop a detatiailed model. I was limited to certain detail and whatever modelling I wanted to do, the time was cut in half using Gmax. Gmax is a very challenging program, but will take your creativity to the next level. I recomend using both programs, but keep maybe FSDS as a priority and slowly use Gmax here and there to explore what capabillities you can achieve. To me FSDS is like the apple of design programs as Gmax is the pc. Hope this insight helps...