I've been running both now for some time, FoF has more songs, but doesnt look as good as GZ.
FoF as mentioned befor, you cannot lose/get boo'd off the track, which kinda makes it no fun.
GZ looks pretty good, and seems to be more on beat. Another great thing about GZ is all the songs have all difficulty levels, whereas FoF usually only have 1 or 2.
GZ has star power as well, but FoF doesn't.
As far as getting the guitar working, I use XBCD driver,
http://www.redcl0ud.com/xbcd.html , and have it configured with that. although both are a real pain to properly get working 100% its well worth it.
Here is a video of both in action on my cab.
[youtube]3I15iwhLo4s[/youtube]