Perhaps the 2012? It can run MacOS Mountain Lion up to Catalina. The quad-core 2.6ghz i7 had very respectable performance in its day, roughly comparable to the base 2018 i5 Mini. Maximum RAM was 16gb. Still use mine as a fileserver. There was also a 2.3ghz quad that was only slightly slower. These are pretty inexpensive today.
Technical specifications for the Mac mini "Core i7" 2.6 (Late 2012). Dates sold, processor type, memory info, hard drive details, price and more.
everymac.com
I'd forget the 2014 Mini, the 2012 quad was about 50% faster than the top-spec 2014 dual i7 (no quad mini's in 2014).
I don't know anything about CS6 though. Is this only a 32-bit compatibility issue? If so, the 2018 Mini can run Mojave and the hex-core i7 CPU is at least twice as fast as the 2012 quad, plus other improvements that make it much faster, plus a max of 64gb RAM. Not sure if it can be rolled back to Mojave after being upgraded to newer versions of MacOS though.
Technical specifications for the Mac mini "Core i7" 3.2 (Late 2018). Dates sold, processor type, memory info, hard drive details, price and more.
everymac.com