So what I'm about the only stingy person here??
Nah. IMHO the issue might be that the question is far too broad......
The question is "what have you used"
Well that's a bunch. Too long to list, most of no interest and long ago deleted.
First, lets separate VSTi from VST, or virtual instruments from other plug ins.
For example. The vast majority of free VSTi are virtual synths. I cant really address that because I am not into virtual synths. How do I rate them when I don't really much care for any of them free or not?
I have tried many, run through the sounds and deleted every one. There are NO third party virtual synths installed on my computer. so....
been impressed by none. Its just not my thing. I accept that.
I do think there are some great sampler based instruments, but so far, none
of the free
ones have really impressed me much. Maybe if I produced EDM or something, I dunno.
Zampler demo was kind of cool for example. Didn't fit into anything I am interested in really. So far anyway. I don't use it so I deleted it.
I had to nudge my "stingy" butt up from free to inexpensive to get satisfactory string pads and such to be honest, and even then.......
I guess I am trying to say the more I demo and test and experience, the more I understand why the better ones aren't free.
And I shy away from much in depth discussion of third party mixing plug ins here, unless the inquiry is pretty specific.
Reason being that I don't want to contribute to the common misconception that people really need third party plug ins to improve their mixes. I've found its usually not the case anyway.
Put another way- Many people who haven't really invested the time and effort to learn about mixing are under the impression different or "better" plug ins are the solution.
I have found that those who have put in the time and effort usually have at least some idea what they are looking for and what to expect.
Often, any difference in sound can be very subtle, and more often than not the desireable traits are interface and workflow related. So it can come down to very individual preferences.
Is there room for improvement on the stock plug ins? Yeah, I think so.
Do I know what you want or need? Nope. Not a clue.