Look at the reviews and demo the sets yourself, as much as you can.
In later Panasonic models (at least the VT30) the 50hz issue is very slight to the point you won't ever notice it if not looking for it. The reviews explain it well. Some good reviews: the one by Phil here at avforums, David Mackenzie did a good job too at * and the review at flatpanelshd is also good.
To me false contouring is worse than the 50hz issue (which I don't notice most of the time), but this is mainly because personal preferences and susceptibility. In any case this posterization problems are very mild with good source because part of the problem is the quantization made by the video codec so it gets worse with bad source which would have most of it anyway with other display technologies as well.
Moreover, you will only get the 50hz issue when watching broadcast TV due to its nature. False contouring will be almost non-existent with good quality content, however certain soft gradients are more prone to it and will exhibit the problem even with blu-ray.
Lastly, don't just look for issues, this set does many things right (great blacks, shadow detail, clean image, motion resolution...), so in the end it's a matter of balance and taste, as it is said everywhere, there is no perfect TV (yet, hehe).
