I tried one of those Insigna PDPD42 for a few weeks, but I took it back because I got one with severe IR issues that were just too bad to ignore, even on the low power setting with 50% brightness & contrast settings (which produced a very washed-out & dull looking picture). The IR was immediate and lasted for several minutes at a time. It could be cleared up with the whitewash, only to be right back again with normal viewing content.
With the right adjustment though, the picture itself was not bad at all. Not great, but definitely an improvment over my 32" CRT. If I had to choose between the PDP42 and an LCD, I would still much rather view the Insignia.
However, I also had other minor issues with it such as awful false-contouring, obvious audio lag with my HT gear & poor compatibility with my universal remote.
As it turns out, the LG I have now seems to be basically the same panel, but with a completely different board and processing. So far, I have only seen some very minor IR that vanishes within seconds, which is about what I would expect out of a budget panel like the PG20.
IMHO, there is no comparison between the PQ of the two sets. The LG easliy generates that looking-through-the-window effect with HD sources, and looks OK with SD as well. My remote works fine with it, and the false contouring is minimal to say the least. I actually thought that the Samsung A450 was about as good as the LG in that area, with the Panasonic PX80 showing more banding than any of the sets besides the Insignia.
The PX80 (especially a calibrated one I saw at BB) looks very natural and has good blacks, the Samsung has great color and the LG seems to be sort of in the middle, with good color saturation, blacks that are better than the A450 and maybe even better than the PX80.
Those are just my observations though, and I have heard that if you get a hold of a "good" PDP42 that isn't defective, then I think it is well worth the price they are going for now. On a positive note, I thought the PDP42 looked very good with SD sources, so that may be worth considering depending on the content that will be viewed on it.
As for the other three, I think the Panasonic is still the higher quality set, but the performance and price difference compared to the LG & Samsung are tough to pass up. Even if the Panasonic is "better" and it can be had for the same price (or less) than the other two, I just personally liked the picture on the LG better, so that's the main reason I bought it.
*Oh, and I have had my eye on a nice Denon receiver for a while now, which will work with the optical output of the LG, but thanks for the tip