My personal input when I was looking at 65 4k TVs is Vizo had a pretty low priced 65 and 70in version for 1.5 and 2k respectively.
Initial reviews on the Vizio were lackluster due to overprocessing the image. They did fix with a firmware update, so I was starting to consider it.
I went to 3 brick and mortar retailers who have had nothing but bad things to say about the TVs (i.e. amount of returns), so I decided against it. That and the fact the overwhelming negative feedback on their support made me stay away. I have read that their M seices TVs have received very positive reviews. This was the P Sereies.
Not that Samsung or any other provider is that much better, but if it were me, I would go with Samsung.
In my case however I have always used Sony TVs and have never had an issue. I experimented and picked up an LG for my bedroom and after that experience I will stick with Sony.
It helped that my Dealer got me the XBR65X850B for 2k. I have two XBRs the XBR4 in the family room 2008 (LCD not LED) is still going strong and has a great picture. The XBR929 I have from 2011 is in the same boat. I will stick with what I know