All these are prices you got from SenQ?

Fundamentally for Samsung entry level 4K HDR TVs , they share the same VA panels and are identical in performance . You know one , you basically also know the rest.

From the KU6100 , KU6300 , MU6100 , MU6300 , MU6400 , NU7100 , NU7400 ... etc

They use the same Samsung UHD Dimming with the same pros and cons , amazing contrast levels , mediocre but steady brightness , decent motion features .
Overall I will say these TVs are pretty good . My only major complains remain its HDR performance . The Samsung UHD dimming provide more another layer of contrast improvement on the TV , but at the cost of dimming very small highlights on the screen . But the overall brightness of the HDR screen is still acceptable in a very dark room.
The 6300 series are usually the curved screens . The 6100 & 7100 series are the flat screens , the nu7400 and mu6400 are the flat screens with Wide color gamut supports .
Samsung has removed some features such as bluetooth & voice remote control , 5Ghz frequency WIFI support on the NU7100 this year .
The FX600 and X7000F are strikingly similar . I always find the Sony pictures a little sharper and generate less noise when you stream lower quality videos .
But they are very minor difference and should not be a deal breaker.  Just remember you don't get the 5Ghz WIFI on the Sony if you ever want to stream PC Media directly to your TV.
As a precaution , which I am sure many are tired of reading , the Sony and Panasonic models are IPS TVs , which is more suitable for a brighter & larger room .

Which one better if compare to samsung u7100 since almost the same price