I'm looking for a really GOOD free guitar VST plugin

Before we get started, I'm not looking for bells and whistles like amp options or effects.  I just want a good acoustic/electric guitar VST plugin that's based on physical modeling and not samples.  I'd prefer an acoustic guitar plugin, but would consider one that can do electric or both.  Ultimately, I am using Guitar Rig to add effects.

I've done some research of my own and tried these:

Pling v4:  Has a fair acoustic sound, but not great.

Revitar:  The absolute BEST of the ones I've tried, but I can't seem to get enough sustain out of it.

DSK Akoustic Guitarz:  Not a bad acoustic sound, but didn't have the sound I wanted when I added effects.

Richman 2:  Decent for clav and electric piano type sounds, but I couldn't get a good acoustic guitar sound out of it.

Solo String:  very limited

String Theory:  cool plugin, but not strictly for guitar.  it would take me hours, if not days, to get a decent guitar sound out of it.

String Thing 2:  Pretty good overall, but I don't like the damping controls.  You cannot make the note end when the key is lifted.

Any suggestions?

As a guitarist, I have looked around as well, at the various guitar synths. Most of them, including many of the sampled ones really come up short when compared to a live guitar.

The ones that come close are sampled and require a bit of learning to get the nuances correct on a keyboard.

A company called Indiginus makes one called Strummaker that actuality sounds pretty good. It is sampled however, and the full version only works in Kontakt. I think the free version is a stand alone and it loads as a VST IIRC.

GuitarHacker.  I checked out the Strummaker you suggested and had a question.  This looks like a great tool to help musicians who don't play guitar...play a guitar but with a keyboard.  My question, do you know if this program would work well with a Axon or any other brand of mid guitar control?

I think you missed the word FREE.

BTW, here's the definition of Real-time Physical Modeling:

Virtual circuitry and/or mathematical algorithms used to generate waveforms (i.e. sawtooth, sine, pulse) or sounds of physical instruments (i.e. piano, guitar, voice) "on-the-fly".

No audio samples of any kind are used.

Edit - My problem with both of these is that they're sample based.  They take up quite a bit of disk space.  Also, don't sample based plugins have higher latency than real-time physical modeling?

Actually physical modeling usually has higher latency than samples. It's a real time process where as samples can reside in ram making them nearly instantaneous. True - samples take up disk space far and above most modeled instruments...but disk space is relatively cheap. Both have their place for sure

I doubt if you can find something that is REALLY GOOD and FREE.
You need to compromise on one of those.

My expectations aren't but so high.  I had been using Dreamstation to create an electric guitar sound.  By my standards, it did a decent job with the help of Guitar Rig.  I was just hoping for something a little better.  Revitar 2 would good if I could get the sustain out of it.  Even with Guitar Rig, I can't seem to get enough sustain for longer notes.  With a little fiddling, I could probably get a sound that would satisfy me from a FM synth . . . plus Guitar Rig.

I guess I got a bit carried away looking for a really good acoustic guitar sound.  In reality, it would work with the proper equipment and a thing (don't know what it's called) do dampen feedback from the body, but it's looking like it's just not there otherwise.  I'm keeping Revitar and DSK Akoustic Guitarz for their acoustic sounds, but I've got to find another method for electric guitar sounds.  Perhaps I will try Yellow Tools Independence FREE 2.5.

I've downloaded all sort of soft synths over the past 1.5 years.  An assortment of analog synths (subtractive, additive, modular), FM, PM, hybrids, etc.  I've got over 50 different synths.  I could probably get rid of a handful, but most are pretty usable and most were FREE.

Some of my personal favorites, that aren't packaged with Sonar, are:

Angular Momentum's Table Synth
DSK's Darkness Theory 3
GTG's FM4
GSi's Organized Trio
Pethu's Hahaha CS33
Richard Brooks and the Voltkitchen Group's MiniMogueVA