I've always been a Sony guy and still am. A bit more expensive but top quality and reliability. However, I noticed the difference between tv brands these days is much less than it was 20 years ago.
First, I suggest you stay away from Plasma - if you are leaping from a 500 lb tube, just about any HDTV will knock your socks off and I doubt if you will have any less satisfaction between the leap to either technology.
I am a Sony enthusiast from way back and gave up my 500 lb (seemed like that - unbelievably heavy) Trinitron for a new 55" Sony HD for the living room and a 42" Sony for the bedroom. However, Sony has changed their marketing strategy and just buying the name doesn't guarantee best quantity. Do your homework. I found that the Sony TV's that you see quoted in the discount electronics store was not their premium product. Sony was producing a variety of TV's to capture more of the market. Many of the advertised bargain Sony TV's when I was looking had refresh rates of 60Hz. The refresh rate is the number of times the image is flashed on the screen. In moving video, it translates into the smoothness of the motion appearing on the screen. The larger the screen - the more perceivable the difference. 120 Hz and 240 Hz are desirable (IMO).
Look for the number of HDMI ports. If you are not using an external switching amp, you might have two HDMI ports to share with CATV, Blue Ray/DVD, Playstation and external video /camera./ phone port. If you see a USB on a non-smart TV's - these are OK for pictures but they will not play multimedia files (movies) on external drives.
Smart TV's. My S.O. got a Samsung a few years back and it plays media files as well as many Apps for YouTube, Netflicks, Facebook, games ... I'm not sure if it is compatible with all of the Android Apps. Many smartTVs coming out support Google TV - a very robust and functional app. In the same way some people prefer component systems to the generic one box grouping of entertainment functions - I like my Minix Neo 7 multimedia box plugged into my HDTV. As an Android device - it supports ShowCase, YouTube , basically all Android software. I run Kodi (XBMC) which is an open source home theatre software that has a lot of support because it is available in Windows, iOS, etc. Minix is a brand - there are lots of choices of these Android based boxes. It turns your HDTV into a full Android system.
All my own experiences - but I must emphasize - do your homework, it really pays off.