As far as ease of use, the QSR is a bit easier to use. When paired with a good controller, the QSR can be just as powerful if not more so than the QS8. Also, if you are using a computer to control the synth, the QSR is supreme.
But for the price of the QS8, you will probably not find another synth of its calibur. It is very powerful.
The only downers I have with the QS series are: no arpeggiator (track generator is a weak impersonation), no tempo control for anything, no filter cutoff, resonance, HPF, LPF, BPF, or any other wave controls.
Some of the great things about it: awesome effects - 4 buses per patch, awesome control of many parameters - fully assignable anything to any control number, aftertouch control, 4 assignable cc sliders, digital direct out, pcmcia expansion capability, and so much more...
So hopfull that will help you make a decision.