I am really interested in purchasing a guitar VST that will allow me to make reasonable guitar parts via a MIDI controller. Amplesound has some VST's that look promising. Has anyone use any of their synth's with SONAR?
 
Are there any successful alternatives?

IMO there are better alternatives. I tried the freebie demo from Amplesound and subsequently deleted it from my sample drive. And I don't delete very many things.
 
EAG from Orange Tree Samples is an excellent product, for $150 IIRC, and would be my first choice. Lots of expressive possibilities, and very credible-sounding. Another very good choice would be the Elya Efimov acoustic guitar, which is currently on sale for 75 euros.
 
If your acoustic guitar needs are modest, e.g. not a featured instrument but more rhythm/background support, a real bargain (at a mere $40!) is the Acoustic Guitar Collection from Indiginus. Highly recommended, even if it's not quite up there with the aforementioned libraries.

All of your suggestions require Kontakt, which I don't have. The reviews of Amplesound's offerings have been very good. I agree with you, though, that the demo sucks.

There is a free Kontakt player available from NI if the sample library supports its use.
 
Regards,

Just an update. I purchased the Gibson and the Martin models from Amber Sound and they are both excellent.

I've had pretty good luck using these:  http://www.musiclab.com/