What is your favorite guard to play and why? 

For me it is half guard which has a bunch of sub-sets within half guard itself.  My game can stay close to the same between No-Gi or Gi and I don't lose a large subset of my game immediately without the grips.  It doesn't matter how large my opponent is, I can always wrap my legs around 1 of their legs.   It can slow the game down which is needed when going against good athletes.  Many more.

Also my class is starting up today, Monday 2/23 for No-Gi Study and we will be working on bottom half guard for those interested!