I have the 65" Samsung HU8550 that I purchased at the beginning of this year. It's imperative that you match your viewing distance with the desired resolution and screen size, otherwise you're wasting money.
I sit about 3-4 feet away from mine when I'm viewing/gaming in 4K and it's phenomenal. When I went to Hawaii in Feb I picked up a GoPro and filmed my travels in 4K, that resulting video alone was worth the TV expenditure.
I would also suggest you look at some reviews on the 4K telly's that you're interested in as to see what features matter to you most. For me, the Samsung had the best ratings.
This guy knows his stuff:
http://carltonbale.com/does-4k-resolution-matter/