In terms of $$ for size/ overall value, 55" is the sweet spot in the marketplace right now.
You can get a decent 120Hz LED for $600-700 if you keep your eyes peeled and the latest 3D and Smart TV features do not matter to you. I suppose you can spend money on a Samsung OLED 55" for three to four times the price of a lower priced 55" and the picture will look fabulous -- though that's a lot of money for a 55". You can get a 70" LED for the same price (or less).
I personally think that even the lower end 70" LEDs are still petty awesome. So if you can justify spending 2-3K for one, by all means, fill yer boots. Those in the $4,000-$5,000 range are better of course in that screen size, but at that end of the market? Markup is VERY high. That's a luxury good and priced as such.
4KTV (UltraHD) is not worth it right now as there simply isn't enough content out there (by which I mean to say -- almost NONE) to justify it. In 2-3 years, matters may be different, and in five years they certainly will be. But that's then and this is now. Let someone else play on the bleeding edge. Don't do it.
I would not be buying a Plasma based TV for any reason in the current market -- no matter how low the price. Plasma has a finite lifespan, they are heavy, can be prone to burn-in and they are about to be extinct. Don't bother.
My experience was that, so long as you are looking at a major brand name, the devil will be in the subjective details, not in any major difference in technical specs.
I think that's probably fair. On the lower-end/ close-out models, there are often some issues with some problems with some features of the unit that are worth knowing about, but which need not be deal-breakers by any means.
LG, Samsung, Toshiba and Sony are all solid bands. Panasonic and Phillips are more suspect, but
usually still pretty great. Stick to those six brands, with a heavy bias towards LG and Samsung.
I would not bother much with investing money into Smart TV features as part of the TV purchase if you are a gamer. Those features are good things to have mind you, but a gaming console will offer all of those features plus a LOT more at a reasonable price. Indeed, a VERY reasonable price if you want to simply pick up a PS3 (used or otherwise) for Netflix and to act as a Blu-Ray player. A used PS3 is still the best Blu-Ray player on the market. PS4? Even better (though admittedly more expensive).
Still, if you don't want to bother with a game console for aesthetic reasons, then take the time to check out the Smart TV features of whatever set you are looking at and be sure to GOOGLE IT FIRST for troubleshooting issues. A lot of the time on the cheaper low end 55" LED sets there are
real problems with the Smart TV features on the unit -- that's
why it is being discontinued.
If those issues either don't matter to you because you don't care, or do not matter to you as you have a game console, then all is well. Get a lower end, major brand name 120 Hz 55" TV (many of which are extremely kick-ass TVs) and keep your money in your pocket.
One feature to keep an eye on is the number of HDMI inputs on the TV. Unless you have a Surround Sound Home Theatre Receiver, you may want to ensure you have at least 4 HDMI inputs. More is
always better.
Lastly,
do look into getting an XBMC unit for your TV. Whether you get a sub-$100 cheap Raspberry Pi based unit or a more expensive Intel NUC based unit, or something in between based on the many Android based players - you will LOVE IT.
With a robust broadband connection - there is no better streaming service on Planet Earth than XBMC. (Just Google it, check it out on Youtube and thank me later). It is
the killer app of today's Internet.