Personally for a first synth, I'd shy away from the more complex stuff for sure. And there's definitely some quality stuff in the freeware realm. I've been having fun with the
Cherry Audio Surrealistic MG-1 Plus freebie. It's got pretty simple architecture, and not a ton of controls, but can still do some funky sounds if you really dig into it.
Getting into a bit more complicated emulations of older synths, https://music.fullbucket.de/vst.html (<b>Full Bucket Music</b>) has some nice variety for free. I find the GUIs a bit on the small side though... maybe that's just my failing eyeballs.
DiscoDSP has a free Oberheim OB-X (
OB-Xd) emulation that might be fun. Check the license though... I think it might be free for non-commercial use only.
U-He
TyrellN6 is pretty solid too... nothing overwhelming, but still flexible and sounds great (as to be expected from U-He).
TAL makes good stuff, and their free
Noisemaker got a facelift not too long ago. It might be a little more complicated than something like their free UNO-62, though (though the free version no longer supported).
Also, regarding the recommendation for
Vital ... that's a wavetable synth. It's not even attempting to be a virtual analog at all (though as pointed out, it can sort of do those sounds too, but that's not really where it shines in my opinion). That said, it's pretty rad. That developer does also have
Helm, which is a free virtual analog that might fit your needs without all the extra spectral warping, vocoding, sampling engine, fx rack, and wild modulation potential of Vital.
Of course, if you want something to occupy you for a few lifetimes, frustrate the hell out of you with its learning curve, and overwhelm you with its thousands of free modules, you can always dip your toes into the free
VCV Rack, and follow the amazing tutorials by
Omri Cohen. That guy's channel alone took me from "modular synth? what's that?" to "I'd better cut up my credit card..."
Synths are like string libraries though... it's good to have at least a few of them on hand for different purposes.
Edit to add: If you're just getting into learning synthesis, maybe check out
Syntorial. It's a combination synth/training-course that teaches you the basics of (virtual-)analog synthesis in small, manageable chunks.