Of those sets - the Pan 55UT50 would be my personal choice.
Still, the Samsung has had some nice reviews, and while the LG probably lags behind the other two in terms of overall PQ, it does have the Largest Screen...
What is your viewing distance?
And what is your relative percentages of viewing material?
(Blue Ray vs Other "HD" Material vs SD Material....)
The closer you sit, and the higher your % of Non-Blue-Rays, the more I would consider a smaller panel.
At the same time, the farther away you sit, the more attractive the 60" panel becomes....
There are other considerations to a buying decision, of course, that this is a good place to start.