I never experienced flicker with my 2010 active shutter Samsung 3D plasma but I did not like their changing the tech behind the glasses with the 2011 sets, going from infrared to bluetooth. Their active shutter tech also exhibited more ghosting and the glasses make the image visibly darker. I also didn't care at all for Samsung's support when I ran into a syncing problem with a a couple of my glasses - they wanted to charge my card to look at them even though they were still under warranty.
With my new LG passive, the glasses are light, don't require batteries, are easy to replace (the RealD 3D glasses from the movie theater are 100% compatible with LG passive TVs) and yield a much brighter image. LG's 2D-to-3D conversion also works better than what I've seen on Samsung TVs.
All things being equal, as long as the picture quality is acceptable to you, I'd go for the LG passive. As someone who has invested in and owns both technologies, I just find the passive to give a more pleasing experience and Samsung has, in my experience, dropped the ball in terms of their support for customers who are still in warranty.