Considering you're using PS3 (assumably for gaming), then low input lag is something you should pay attention to. 4k is not recommended at this point, as they bring more input lag, on average. Exceptions apply, though. But also remember, that even the latest game consoles don't currently output anything above 1080p. So 4k will be an empty feature in that regard.
In any case, use this for reference:
http://www.hdtvtest.co.uk/news/input-lag
I would prefer to stay below 20ms, and below 25ms, at a bare minimum. I have a ~35ms set, and the lag is fairly noticeable, especially on fast-paced games.
If you're ok with regular FullHD sets, then go for Sony. But, if you really want 4k, then Samsung seems like the way to go, currently. But whatever you do, DON'T BUY PHILIPS. They are utter amateurs. Not only because of bad input lag levels, but also for very bad product and customer support. I don't think I can stress this enough. Their quality has dropped very dramatically from what it used to be. Consider yourself warned.
But anyway, I haven't seen any good 40" 4k TVs, input lag -wise. But if 48" is ok, then the Samsung UE48JU7500 (
http://www.hdtvtest.co.uk/news/ue48ju7500-201504074038.htm) might be worth a consideration. But it's around £1000 and it's curved.
Also note:
Very few 4k TVs come with a DisplayPort connector. From what I've seen, only Panasonic has included DP, and they start at £1500. So, you will probably need a GPU with an HDMI 2.0 port for 4k@60Hz. IIRC, that's currently only possible with GTX 950-980. The selection will probably increase on the upcoming generation of cards, from both AMD and nVidia.
For a fairly recent thread with similar topic, check this for more pointers:
https://forums.overclockers.co.uk/showthread.php?t=18710016
