Had a private quite recently where I went through some sweeps and sequences in this position.
Who's your favourite Z guard player and why? also any videos/instructionals on the position would also be appreciated, really want to try and understand it as it seems like it could work for me.
Cheers
Robson Moura is the guy to look at. Extensive section on both go and no gi for these guards in super no gi and fusion sets
Robson for sure!
Is there a difference in 93 guard, z guard, and knee shield? I've been playing with a knee shield on my opponents shoulder like Caio Terra. Been using a lot from his DVD. 
TexDeuce -Is there a difference in 93 guard, z guard, and knee shield? I've been playing with a knee shield on my opponents shoulder like Caio Terra. Been using a lot from his DVD.
As I understand it the main difference in 93 guard (aside from the grips perhaps) is that you keep your knee up and pointing to the ceiling blocking your opponents shoulder, rather than across and blocking his chest or stomach. In the Fusion 93 guard DVD Robson stresses not allowing your opponent to force the knee down, which is where you become vulnerable to z-guard/knee shield passes. Can't recommend that DVD enough, totally revolutionized my open guard against kneeling opponents.
Here for knowledge 
Robson is the maestro. Lots of his vids available on asian youtube if you know how to google.