Which TV would you chose for same price? LG 55UF6800 vs Samsung UN55JU6400

Solution
The first comment appears to be accurate:
http://www.rtings.com/tv/reviews/lg/uf6800

FYI, the 120Hz mode is an internal thing, and I suggest applying it only for sports. It creates new frames (one frame per real) thus for example the hockey puck is easier to track in a hockey game, however it creates issues with movies because the applied movie motion blur is optimized for 24Hz (24 frames per second) thus looks wrong at 48Hz (I know we're at 120Hz but it's actually 48 real frames for a movie, or 24 frames if not using the 120Hz motion smoothing mode).

(A 24Hz movie, or 30Hz video ends up as a 60Hz signal going into the HDTV. Then, if you apply 120Hz mode the computer in the HDTV analyzes several frames then creates NEW ones that fit...
The first comment appears to be accurate:
http://www.rtings.com/tv/reviews/lg/uf6800

FYI, the 120Hz mode is an internal thing, and I suggest applying it only for sports. It creates new frames (one frame per real) thus for example the hockey puck is easier to track in a hockey game, however it creates issues with movies because the applied movie motion blur is optimized for 24Hz (24 frames per second) thus looks wrong at 48Hz (I know we're at 120Hz but it's actually 48 real frames for a movie, or 24 frames if not using the 120Hz motion smoothing mode).

(A 24Hz movie, or 30Hz video ends up as a 60Hz signal going into the HDTV. Then, if you apply 120Hz mode the computer in the HDTV analyzes several frames then creates NEW ones that fit in between the old ones. So, for example, if a hocky puck was travelling left to right it will make a new frame that puts the puck in between two of the original frames according to how it's accelerating.)

I'd still suggest looking at Amazon because there's usually good customer feedback, but I doubt I'd change my mind.
 
Solution
If you're going to watch a lot of movies invest in a 120 Hz TV, if not 60 Hz + interpolation is fine and unless you put two side by side it won't bother you. The main difference between the LG and Samsung is contrast. If that's your budget, then either these will be better buy:

http://www.amazon.com/Sony-XBR55X810C-55-Inch-Ultra-Smart/dp/B0148OZLOS/ref=sr_1_1?ie=UTF8&qid=1453592555&sr=8-1&keywords=Sony+X810C

4k
120 Hz native
Handles scaling really well
Low input lag (35 ms)


or


http://www.amazon.com/gp/product/B00R45XC0Y?tag=rtings-tv-bs10b-20&ie=UTF8

1080
120 Hz
Low input lag (37 ms)


In my opinion, it doesn't make any sense to buy 4k TV's just yet, until the manufacturers have decided what the new standards should be, and not come up with something new every week. Though I do think 120 Hz native is mandatory if you watch a lot of movies to ensure 24 * 5 playback, rather than the judder that otherwise happens on 60 Hz, as explained by photonboy. Not only that, but you will also benefit from the faster pixel times, so less ghosting while playing games, etc.





All the best!