Cobra Kai advocated standing passes whenever possible. I think this is mainly because they have a lot of guys who want to do MMA as well. But it certainly has other benefits - such as the bottom guy not being able to take your back, triangle, or armbar you.
Personally I use both, but spend 60-70 of my time passing on the knees. Mainly because my *PERSONAL* style is a very tight game. I pass with pressure.
I have particular trouble defending my open guard against Cobra Kai guys because they prefer to stand. You have to either immediately go into Xguard, leglocks, or stand up. Because if I sit there for any period of time they slice through my guard and I am immediately put on defense trying to recover guard, get a good half guard position, or get to all fours.
I use the standing pass because I feel too vulnerable to being triangled in the kneeling pass. My instructor usually teaches the standing pass.