FWIW, I had to choose two for the Hybrid Madness offer when I bought the Analog Factory Experience. I searched the boards for advice also but in the end it came down to downloading the demos to compare and trying to fill the "audio gaps" in my collection.
I knew I wanted the Oberheim, so it was a toss between the Arp 2600 and the CS-80.
I found that although I liked many of the CS-80 sounds (BLADE RUNNER!!!), I had most of the patches I really wanted already in AFE, and so it came down to which I would enjoy programming more. Which had to be the 2600 for me...
It's a personal preference and I would say but you need to get the most recent version of the demos to find out for yourself.
Plus I just got the free miniMg so thanks Arturia!