I have both, or at least I did at one point because I can't find the other one right now. iirc, the guitar tab one is a bit more like a score - there are certain songs where a lot of different parts are listed like strings, organ, bass, it depends on the song. I'd tell you more if I could locate my copy.
it really depends on what you're looking for. for instance, the PVG book has piano arrangements of every song, but the guitar tab version only shows piano parts if the song happens to have a piano part. if you don't mind working around the constraints or if you just want to see some of the individual parts, order the guitar tab book. if not, keep the PVG one. there's advantages and disadvantages to both. I personally really like the arrangement of US in the PVG book