Making virtual instruments real and believable is a matter of having faithful sound banks but... while this is enough for "keys" (pianos, organs, synths, etc.), it's only a starting point for guitars if you are playing them through a keyboard.
Due to that, being that I carry out some arrangements and transcription of pop and jazz music for the band I am part of - as an enthusiast, not as a professional! - and that I can play keyboards only, I have found over the years that the best results are achieved through software packages that provide you with the knowledge of how a guitar has to be played (especially for grooves), while you only need to put in place the right chords and select the grooves within a library. In this perspective, I recommend a couple of products by a famous German company: Strummed Acoustic and Scarbee Funk Guitarist. They are sample-based. I suppose there are dozens of equivalent products out there, but I had the chance to try only these two and they were really effective for me.
I don't know what kind of music you play but I hope to have provided you with some ideas.