I started with EQ5 then upgraded to EQ6. I found that it was fun to design quilts, even made one or two of them. What I did find useful was the section telling how much yardage you would need for the quilt. It breaks it down into colors and that is very handy. However, now, when I am designing a simple quilt, I usually just sketch it out on paper and figure it. For me, the use I receive from it is what I expect. Basically, EQ will give you back what you are willing to put into it. It is fairly easy to learn but time consuming. Lots of little details.
Frankly, unless you decide to design a lot of applique blocks which is not the easiest thing to do, you would be fine with EQ6 or even EQ5. Good luck!!