Both libraries include a Solo Engine and a Strumming Engine.
The Instant Guitar Series is aimed towards giving you instant strumming patterns using X Legato to change chords, where the Advanced Guitars allow you to create your own custom strumming patterns using our Custom Strumming Engine.
The Advanced Guitar Series also offers more articulations within the Solo Engine, as well as a Solo Guitar Legato, where the Instant Guitar has a both sustains and sound designed sustains.