I started with EQ 3 and each version gets better. Also the program has to be updated to match the updated computers. Each new update has tweaks and add ons that maybe were not possible for the old version. I suspect the newer versions will be more online and more in real time, that will be great to be able to show your work to other EQ users and design together with others.
My computer will not run EQ 3 or 4 now. EQ 5 works fine but there are limitations that EQ 6 does not have.