I have two, a 63" and a 55" inch. Both, we got from Costco at great deals. Both are 1080p, have a solid standard cable pic, great hi-def pic, and amazing Blu-Ray pics. Sound is okay, but that's easy to fix (in our game room, we have a wireless soundbar).
I don't know anything about the 4k tvs other than I have heard that there still isn't much content to watch on it. That, and this is the most important part......Wait as long as you can to buy any tv. They get better and cheaper every day for the most part. I used to read avs forum religiously, I was thinking about getting a projector for my living room.. then I quit gaming, reclaimed my life and bought a mountain bike. Seriously considering canceling my dish. Still love movies and rent blurays from redbox for 1.50 so I still want a decent tv, just not as into it as I was.
4K TV upscales blue ray so it looks better than HD. 4x as many pixels. They could just double each pixel/color in both height and width, or they can do an average of the pixel to the left and right, for example.