The LG is a lot of TV for the money, but it really comes down to what you want from a TV.
As far as 3D and Smart TV functionality the LG is the best value. However, the 2D picture is a bit hit and miss for a lot of people. The AVforums is probably the best place to research this aspect further. I can't comment on the LG's issues, as I have only seen them in Currys, but I did notice one of two things that put me off, but that's me.
The Panasonic I believe is a similar panel to the LG (IPS) so you can expect some similar issues, such as slightly weak blacks depending on lighting environment and clouding - but all TVs have this to some degree. Like the LG it also has passive 3D, which in my view is superior to active 3D in terms of comfort for most people's eyes. The only thing that Panasonic lacks compared to the LG is the Smart TV functionality, as it is not as developed as the LG.
The Samsung will pretty much have the best 2D picture of the 3, as it uses a PVA panel which is better at producing deep blacks. It also has a better technology at handling fast motion, and if you want to turn on all the features, can achieve 1080 lines of resolution in motion where most LED/TVs can only get 300! The other great thing, is the Smart TV side of the Samsung is just as accomplished as the LG. The only thing it comes down to is preference to the interface.
Overall, it really depends on what you looking for and how much you are willing to spend to get the features you want.