I mainly use synths like Massive, FM8, etc, but I think I could get some interesting results with VSTs that are instrument-specific, because they have different parameters. For example Tension has "stiffness", "friction", "force" and other parameters like that. I want to try some VSTs that have those sorts of parameters.

I downloaded Piano One, which is free, and has a nice high quality and realistic sound, but there isn't much variation you can do to it.
So what are the best VSTs you know of that work like this for piano, strings, and/or brass? I would prefer free ones obviously, but I would maybe be down to buy one as long as it's a reasonable amount of money and it's good.
PS: I am especially looking for one that does saxophone. Also, is this sorta the point of big-name samplers like Kontakt that come with big sample libraries? I never really saw the need to get a sampler other than Ableton's built in one. Is this why people like Kontakt so much?