the reason i place sony in the lead is that i believe they are still the only company which actually stocks replacement parts. samsung seems to be reputable as well. lg products are okay but their customer service is awful or so i've been told.
vizio, olevia, and pretty much any of the budget televisions are not worth your time. while they may be cheap and some people say they have had good luck with them if you do have a problem getting parts might be more involved than you would think. i have a relative who was a repair tech for 20 years.
if you want 3d you will want a 3d capable tv. if you want internet on the tv then you need the funtion. led backlit tvs will save quite a bit on your power bill over ccfl. if you plan to use the tv with a computer for gaming then you want a 60hz tv not 120 or 240 or you need to make sure the 60hz mode (game mode) actually works in the model you like.
for $600 you can get a 40" 60hz led sony bravia. you might have to look around for a sale or coupon but it is possible. it might be a barebones model (no 3d, no internet tv) but definitely a good choice.
i dont know if there is any best tv. ever person likes different models and brands depending on past experiences with the brands and personal perception (our eyes are all slightly different).
What if I told you that you should not need replacement parts? However, sometimes things happen. I have 2 Samsungs and they are doing pretty well. However,they might be overpriced. I purchased my last one online from VANNS. It was only a 40" and it came in the fatory box. It seems in the last year that some prices may be coming down. Personally I dont care for 3D and I prefer LCD. The prices are better and I think the LCD's have plenty of quality. Also I prefer to keep the refresh rate to 60Hrz.
HDTV's try to play video at the given rate of 28-30 frames per second for normal video. That is a standare speed for full motion video. If the Hrz are too high of a refresh rate like 120 or 240, then the HDTV's use a program that trys to insert images or screens inbetween to smooth out the vdeo for the missing screens. This causes the video to get choppy. So then people adjust these faster TV's to change how it runs in an attempt to get a better picture. Thus they are wasting their money on technology they are defeating. Sounds crazy right?
A 3D video needs at minimum a speed of 240hrz to do 3D. I dont like 3D, so I dont care. I consider it a fad. I am what you might call a late implementor. Maybe the video will get better. I have seen a couple of places on the Internet that normal video should be at a differnt speed like say 45 frames per second. Sometimes I think they just pick refresh rates of 60Hrz because it is a round number. Probably the work of some evil engineers.
So what else to look for?
Inputs and outputs?
I like a lot of HDMI inputs at least 4
Another good think is to have a couple of RCA style inputs like component video Sometimes you need some backwards compatability.
Then you may want the obligatory optical Audio out.
Ethernet for Network access.
A few USB plugs for flash drives and maybe wireless dongle.