Roland GAIA2 - Drive Makeup Sensitivity 

That's a great question and a bit challenging to answer, to be honest! Both are great to learn synthesis on because of their knobby design. Lots of parameters accessible and controlled with the hardware. I think the System-8 is more complex in that the different plugouts activate different knobs so that could get confusing. But then, the Juno-X has ZEN-Core and model expansions too. Both are superb bits of gear and either will help folks learn. They're priced almost the same. Juno has an extra octave. System-8 is ACB. Juno has iArp, System-8 has classic arp. ALl said and done I'll go with the Juno-X as it is more left to right. System-8 is left to right, but up and down too!