this

Samsung, and Panasonic plasmas have the best image quality. You can even go cheaper and buy an LG and still get a better image than any LCD/LED in anywhere near the same price range.

any Samsung is good enough

He is asking for a gaming television and Sony W800 and W900 series have fastest response time. Twice as fast as a plasma in the same class. http://reviews.cnet.com/8301-33199_7-57589240-221/best-low-lag-hdtvs-for-serious-gamers/

Still Sony does has the best TV available for an amazing price. I have not seen any television better then the 55X9005 which is 4500 euros here. Though I know that W900 series is expensive it has still the best picture in it's class. If you don't care about the best Smart TV options (which Samsung has in my opinion) and only picture quality for a LED then Sony is a great choice. 

How bad are Plasma burn-ins nowadays?

Plasma TVs have 0.01ms response time, which is probably the most important thing when talking about gaming TVs. No LCD/LED can compete with that, it's a limitation of their technology. Input lag is also very important, but since response times in LCDs are quite high, Plasmas TVs still have the edge when it's about gaming.

Nah. They beat even the CRTs with their best sets. 

I've used my plasma (2010 model) as a PC monitor for the past 3 years and the worst I've ever gotten is the tiniest bit of image retention which is cleared by running white noise or a black/white scrolling pattern.  My new plamsa (2013) hasn't shown even the slightest tendency to retain images.

Plasmas are still the best TVs and I don't think there is much debate about this.  Plasmas have the best black levels, colour, contrast, motion handling and 3D (generally).  The power cost difference is going to amount to several dollars per year and unless you are watching the TV in direct sunlight, the lack of brightness compared to LCDs is not an issue.

This year's Panasonics (ST/GT/VT) and the 8000 series Samsung plasmas are killer.  Sony's flagship LED this year is also fantastic (can't recall the model number).  I would hesitate to drop $2000 on a TV just because it's input lag is the lowest.  What you want is the best TV you can get for your money, all things considered, while ensuring you don't compromise on input lag.

For my money I'd go a 65inch Panasonic ST60, or a 55-60inch VT60, depending on what prices are like in your area and your preference for size versus ultimate quality.

Edit: One addendum to the above.  Plasmas are still supposed to be treated gently for the first 100 hours or so as it takes a while for the phosphor to stablise.  This means not running the TV at the highest brightness or contrast levels (not that you generally need to) or with fixed images for extended periods.  It's possible that failure to do this could cause issue with your panel but again this is more a theoretical risk.

Again, clearly plasma are the best until oled is affordable. led is horrible and laughed upon by anyone serious about pq. I'm getting the vt60, but for someone on a budge, the  s60 is incredible value (st60 if input lag isnt a big deal)