Maybe he’s a bit… abrasive, but Jexus has a lot of old synth demos and also reviews on his website. He was dormant for a few years, but his older stuff is mostly 80’s/90’s/00’s. The sounds he can coax out of any synth will sell you on it, but his commentary is also useful.
As for me, I <3 the Blofeld, and second the recommendation of the Reface DX… its modulation capabilities are somewhat restricted, but embracing them can lead to fantastic results. 
I used a ESQ-1, and I think it has a really cool interface, but I didn’t fall in love with it. (Heck, if anyone from Pittsburgh wants it, hit me up.)
The Casio HT-700 is a fun instrument, but frustratingly limited, and with a really annoying interface for programming (like an Alpha Juno where the dial remembers what position it’s at and has hard stops, so you always need to find your place in the parameter list because it’ll be different once you’ve changed the value.) If you can get one cheap, go for it.
Lastly, my old roommate at one point was given an SY77 with some missing keys that had sat out in the rain as payment for reparing a Juno, and… I loved that thing. Sure, it’s a ROMPLER that I never wanted to program, but the presets and the sounds on it are just good and musical. <3
