There is a difference in panels, good or bad is something of a matter of the end product and not just the panel. The electronics involved, the filters, if any. In most forums I read is the plasma panel of panasonic is the best, probably a factor of them putting the max. r&d into the plasma panel, while the other two are primarily lcd/led players.
The other key differentiating factor is that panasonic gives 3 years warranty while lg and samsung give 1 year warranty. However, dealers like croma do give extended warranty at a price.