I have a samsung plasma, and to be honest, I'm not really happy with it. The processing of the image seems to introduce some terrible artifacts. I have upgraded the firmware several times, but no firmware seems to fix it.
This may be that I got a dodgy panel, or maybe it's just with plasma, but I'd just be careful if you go samsung.
I would like to try out the LG to see how the viewing angle is, because I feel that the shutter glasses are a pain. They degrade the picture terribly and tend to go out of sync when the scene changes, or there are bright flashes from the TV picture. Even with the halved resolution of passive, if the viewing angle wasn't too bad and the ghosting is on par with active, I'd probably go the passive.
One other thing to think about is sound. I believe that neither of these sets have particularly good sound, so you will probably need a surround receiver. Make sure you get one that supports HDMI 1.4a as a minimum. This will save you a whole lot of trouble. Even though you can get the audio signal from the TV and connect that to a surround, at least with the samsung, it is only stereo.
I'd suggest going to a few stores and trying a lot out first. And remember that you will be even more fussy about any imperfections when you get home.
Let us know how the hunt goes.