Chiming in a bit late, but better than never.  I find that FSDS is MUCH easier to use than Gmax.  However, FSDS is severly limited in several aspects.  You can modify the interface much more in Gmax, Gmax has more primitives, and in general it is a lot more detailed than FSDS.  Having said that, as a first time builder, FSDS is a life saver.  If I hadn't gone out and got FSDS, I never would have gotten as far on this plane as I have.  In the future, I will most likely learn Gmax, but I must give FSDS credit.

Oh, and in FSDS, you can only undo 1 level.  They really need to fix that... 

Ok here's my quarters worth(used to be two cents but everything has gone up)Iv'e built 3 mdls with Gmax(PC_47H,Flyingsub,and the Jupiter2),and it has been very trying and very very rewarding.Gmx lets you do more delicate and percise texture placing,also it's alot easier and faster to cut out windows, doors, and ect...also you can extrude,bevel and soforth. ONCE YOU LEARN !It takes alot of PRACTICE and TRIAL and ERROR.I used FSDSv1 when I first started and built a very nice mdl (PC-45H for CFS2 it's here on Pg33).Now I'm trying FSDSv2, and it has IMPROVED GREATLY!I like the ease of how it works,but then I miss my BOOLEN and EXTRUDE.I also like how it has the variables that you can manipulate for effects.I think both programs are very good (ONCE YOU LEARN THEM).If you are short on money and have FS2004 use Gmx,if you have trouble with complicated programs and have about 60 bucks use FDSDv2.If you need help with either one look here,I know I'd have been alot longer building mdls if it weren't for all the people who are very knowing in this Forum.This is just my opinion.Remember no matter which one you use PRACTICE,PRACTICE,PRACTICE!
Best Regards,Ronnie